UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                  SCHEDULE 13D
                   Under the Securities Exchange Act of 1934
                               (Amendment No. 2)*


                                  AEROGEN, INC.
--------------------------------------------------------------------------------
                                (Name of Issuer)

                     Common Stock, par value $0.001 per share
--------------------------------------------------------------------------------
                         (Title of Class of Securities)

                                    007779309
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                                 (CUSIP Number)

                                                     with a
                                                     copy to:
         Mitchell D. Kaye, Manager                   Steven E. Siesser, Esq.
         Xmark Asset Management, LLC                 Lowenstein Sandler PC
         301 Tresser Blvd., Suite 1320               65 Livingston Avenue
         Stamford, Connecticut 06901                 Roseland, New Jersey  07068
         (203) 653-2511                              (973) 597-2500
--------------------------------------------------------------------------------
                 (Name, Address and Telephone Number of Person
                Authorized to Receive Notices and Communications)

                                February 23, 2005
--------------------------------------------------------------------------------
             (Date of Event which Requires Filing of this Statement)


If the filing person has previously  filed a statement on Schedule l3G to report
the  acquisition  that is the subject of this  Schedule  13D, and is filing this
schedule  because of Sections 240.13d-1(e),  240.13d-1(f) or 240.13d-1(g), check
the following box. [ ]

Note:  Schedules  filed in paper format shall include a signed original and five
copies of the schedule, including all exhibits.  See Section 240.13d-7 for other
parties to whom copies are to be sent.

* The remainder of this cover page shall be filled out for a reporting  person's
initial filing on this form with respect to the subject class of securities, and
for  any  subsequent   amendment   containing   information  which  would  alter
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the  Securities  Exchange  Act of
1934 ("Act") or otherwise  subject to the liabilities of that section of the Act
but  shall be  subject  to all other  provisions  of the Act  (however,  see the
Notes).




Cusip No.         007779309
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1.  Names of Reporting Persons.  I.R.S. Identification Nos. of above persons
   (entities only):
                       Xmark Asset Management, LLC
                               13-3954392
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2.  Check the Appropriate Box if a Member of a Group (See Instructions):
         (a)                  Not 
         (b)               Applicable
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3.  SEC Use Only
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4.  Source of Funds (See Instructions):  WC
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5.  Check if  Disclosure  of  Legal  Proceedings Is  Required Pursuant  to Items
    2(d) or 2(e):                 Not Applicable
--------------------------------------------------------------------------------
6.  Citizenship or Place of Organization:  New York, United States
--------------------------------------------------------------------------------
    Number of                      7. Sole Voting Power:                  *
                                      ------------------------------------------
    Shares Beneficially            8. Shared Voting Power:                *
                                      ------------------------------------------
    Owned by
    Each Reporting                 9. Sole Dispositive Power:             *
                                      ------------------------------------------
    Person With                   10. Shared Dispositive Power:           *
                                      ------------------------------------------
--------------------------------------------------------------------------------
11. Aggregate Amount Beneficially Owned by Each Reporting Person:     1,133,330*
--------------------------------------------------------------------------------
12. Check if the Aggregate Amount in Row (11) Excludes Certain Shares
    (See Instructions):          Not Applicable
--------------------------------------------------------------------------------
13. Percent of Class Represented by Amount in Row (11):   18.8%*
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14. Type of Reporting Person (See Instructions):  IA
--------------------------------------------------------------------------------

* Xmark Asset  Management,  LLC, a New York limited  liability  company ("XAM"),
serves as investment  manager for each of Xmark Fund,  L.P., a Delaware  limited
partnership  ("Xmark  LP"),  and Xmark Fund,  Ltd.,  a Cayman  Islands  exempted
company  ("Xmark Ltd").  In such  capacity,  XAM possesses the power to vote and
direct the  disposition of all securities  held by Xmark LP and Xmark Ltd. As of
February  23,  2005,  Xmark LP is the  holder of 50,337  shares  (the  "Xmark LP
Preferred") of the Series A-1 Preferred  Stock,  par value $0.001 per share (the
"Preferred  Stock") of Aerogen,  Inc., a Delaware  corporation  (the "Company"),
which are presently  convertible  into 503,370  shares of the  Company's  common
stock, par value $0.001 per share (the "Common Stock"). As of February 23, 2005,
Xmark  Ltd is the  holder  of 62,996  shares  (the  "Xmark  Ltd  Preferred")  of
Preferred Stock,  which are presently  convertible into 629,960 shares of Common
Stock.  The  terms  of the  Xmark  LP  Preferred  and the  Xmark  Ltd  Preferred
originally precluded each of Xmark LP and Xmark Ltd from converting the Xmark LP
Preferred and the Xmark Ltd Preferred if the conversion  thereof would result in
Xmark LP, Xmark Ltd and/or  their  affiliates  beneficially  owning in excess of
4.99% of the Company's  outstanding  Common Stock  following any such conversion
(the "Issuance Limitation"). Each such Issuance Limitation was waivable by Xmark
LP and Xmark Ltd, respectively, providing 61 days' advance written notice to the
Company.  On  November 3, 2004,  Xmark LP and Xmark Ltd each  provided a written
waiver of the  Issuance  Limitation  to the Company with respect to the Xmark LP
Preferred  and the Xmark Ltd  Preferred.  As a result  of this  waiver  and as a
result of the fact that XAM  possesses  the sole  power to vote and  direct  the
disposition  of the securities  described  above,  for purposes of Reg.  Section
240.13d-3,  XAM may be deemed to  beneficially  own  1,133,330  shares of Common
Stock,  or  approximately  18.8% of the shares of Common Stock deemed issued and
outstanding as of February 23, 2005.






Item 5.   Interest in Securities of the Issuer.
          ------------------------------------ 

          Item 5 of the  Schedule  13D is hereby  amended  and  restated  in its
entirety as follows:

          Based on information  reported by the Company in its Form 10-Q for the
fiscal quarter ended September 30, 2004,  filed with the Securities and Exchange
Commission  on November 15, 2004,  there were  4,884,829  shares of Common Stock
outstanding  as of November 5, 2004.  As of February 23,  2005,  Xmark LP is the
holder of 50,337 shares (the "Xmark LP  Preferred")  of the Series A-1 Preferred
Stock,  par value $0.001 per share (the "Preferred  Stock") of Aerogen,  Inc., a
Delaware  corporation  (the  "Company"),  which are presently  convertible  into
503,370  shares of the Company's  common stock,  par value $0.001 per share (the
"Common  Stock").  As of February  23,  2005,  Xmark Ltd is the holder of 62,996
shares (the "Xmark Ltd  Preferred")  of  Preferred  Stock,  which are  presently
convertible into 629,960 shares of Common Stock.

          The  terms of the  Xmark LP  Preferred  and the  Xmark  Ltd  Preferred
preclude each of Xmark LP and Xmark Ltd from  converting  the Xmark LP Preferred
and the Xmark Ltd Preferred if the conversion  thereof would result in Xmark LP,
Xmark Ltd and/or their affiliates  beneficially owning in excess of 4.99% of the
Company's  outstanding Common Stock following any such conversion (the "Issuance
Limitation").  Each such  Issuance  Limitation is waivable by Xmark LP and Xmark
Ltd, respectively,  providing 61 days' advance written notice to the Company. On
November 3, 2004,  Xmark LP and Xmark Ltd each provided a written  waiver of the
Issuance  Limitation  to the Company with respect to the Xmark LP Preferred  and
the Xmark Ltd Preferred.  As a result of this waiver and as a result of the fact
that XAM  possesses  the sole power to vote and direct  the  disposition  of the
securities  described above, for purposes of Reg. Section 240.13d-3,  XAM may be
deemed to beneficially  own 1,133,330  shares of Common Stock, or  approximately
18.8% of the shares of Common Stock deemed issued and outstanding as of February
23, 2005.

          During  the sixty  days  prior to  February  23,  2005,  there were no
transactions in Common Stock, or securities convertible into, exercisable for or
exchangeable for Common Stock, by XAM or any person or entity  controlled by XAM
or any person or entity for which XAM  possesses  voting or  investment  control
over the  securities  thereof,  except that Xmark LP and Xmark Ltd sold:  (1) on
January 19, 2005, warrants to purchase up to an aggregate of 1,666,660 shares of
the Company's Common Stock for an aggregate  purchase price of $383,331.80;  (2)
on January 24,  2005,  53,333  shares of the  Company's  Preferred  Stock for an
aggregate  purchase price of $960,000.00,  in each case, as more fully described
in Item 6 of this Amendment No. 1 to Schedule 13D; and (3) on February 23, 2005,
91,309 shares of Common Stock for an aggregate purchase price of $164,355.48. On
or about  January 20, 2005,  XAM was notified that the Board of Directors of the
Company had declared that Xmark LP would  receive  15,149 shares of Common Stock
and Xmark Ltd would receive  18,958 shares of Common Stock from the Company,  as
payment in lieu of cash  dividends on the Preferred  Stock for the quarter ended
September  30, 2004.  On or about  February 4, 2005,  XAM was notified  that the
Board of  Directors  of the Company  had  declared  that Xmark LP would  receive
16,996  shares of Common  Stock and  Xmark Ltd would  receive  21,270  shares of
Common  Stock from the  Company,  as payment  in lieu of cash  dividends  on the
Preferred Stock for the quarter ended December 31, 2004.

Item 6.   Contracts, Arrangements, Understandings or  Relationships With Respect
          to Securities of the Issuer.
          ----------------------------------------------------------------------

          Item 6 of the Schedule 13D is hereby amended by adding the following:

          Pursuant to the terms of a Securities Purchase Agreement,  dated as of
February 23, 2005, by and between Xmark LP and OTATO, L.P., Xmark LP sold 40,556
shares  of the  Company's  Common  Stock  for an  aggregate  purchase  price  of
$73,000.08,  or a purchase price per share of $1.80.  Pursuant to the terms of a
Securities  Purchase  Agreement,  dated as of February 23, 2005,  by and between
Xmark Ltd and OTATO,  L.P., Xmark Ltd sold 50,753 shares of the Company's Common
Stock for an aggregate  purchase  price of  $91,355.40,  or a purchase price per
share of $1.80.

          The  descriptions of the transactions and agreements set forth in this
Amendment No. 1 to Schedule 13D are qualified in their  entirety by reference to
the complete  agreements  governing  such  matters,  which are  incorporated  by
reference  or  attached  to this  Amendment  No. 1 to  Schedule  13D as exhibits
pursuant to Item 7 hereof.






Item 7.   Material to be Filed as Exhibits.
          --------------------------------

          Item 7 of the Schedule 13D is hereby amended by adding the following:

          9. Securities  Purchase  Agreement,  dated as of February 23, 2005, by
and between Xmark LP and OTATO, L.P.

          10. Securities Purchase  Agreement,  dated as of February 23, 2005, by
and between Xmark Ltd and OTATO, L.P.







                                    Signature
                                    ---------

          After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information  set forth in this statement is true,  complete and
correct.


                                            As of February 23, 2005

                                            XMARK ASSET MANAGEMENT, LLC


                                            /s/ Mitchell D. Kaye 
                                            ------------------------------------
                                            Mitchell D. Kaye, Manager


Attention:  Intentional  misstatements  or omissions of fact constitute  Federal
criminal violations (See 18 U.S.C. 1001).





                                                                       Exhibit 9

                          SECURITIES PURCHASE AGREEMENT

          This  SECURITIES  PURCHASE  AGREEMENT,  dated as of February  23, 2005
(this  "Agreement"),  is by and between  OTATO,  L.P.,  a Grand  Cayman  limited
partnership  (the  "Purchaser"),  and  Xmark  Fund,  L.P.,  a  Delaware  limited
partnership ("Seller").


          WHEREAS,  the Seller owns 40,556 shares (the "Shares") of Common Stock
(the "Common  Stock") of AeroGen  Inc.  (the  "Issuer"),  which shares of Common
Stock  are  subject  to  a  currently  effective   registration  statement  (the
"Registration Statement"); and

          WHEREAS,  the Seller wishes to sell the Shares to the  Purchaser,  and
the Purchaser is willing to purchase the Shares from the Seller.

          NOW,  THEREFORE,  in consideration of the foregoing and the covenants,
agreements  and  warranties  contained  herein,  the  sufficiency  of  which  as
consideration is hereby acknowledged, the parties agree as follows:

          1. Definitions.  When used herein,  the following terms shall have the
indicated meanings:

          "Encumbrance"  means  any  pledge,  hypothecation,  assignment,  lien,
restriction,  charge, claim, security interest, option, preference,  priority or
other preferential arrangement of any kind or nature whatsoever.

          "Transfer  Restriction"  means,  with respect to any security or other
property,  any condition to or  restriction on the ability of the holder thereof
to sell,  assign or otherwise  transfer  such  security or other  property or to
enforce the provisions  thereof or of any document related thereto,  whether set
forth in such  security  or other  property  itself or in any  document  related
thereto or arising by  operation of law,  including,  without  limitation,  such
conditions or restrictions  arising under federal,  state or foreign  securities
laws or under contract.

          2. Sale and Purchase.

          (a) On the  Settlement  Date,  the Seller shall sell to the Purchaser,
and the Purchaser shall purchase from the Seller (the "Transaction"), the Shares
for an aggregate purchase price (the "Purchase Price") of $73,000.08 in cash.

          (b) On the Settlement Date, the Seller shall deliver to the Purchaser,
at the address set forth in Section 8 hereof, the Shares, duly endorsed.

          (c) On the Settlement  Date, the Purchaser shall deliver to the Seller
the  Purchase  Price by wire  transfer  of  immediately  available  funds to the
account designed in writing by the Seller.




          3. Representations, Warranties and Agreements of the Seller.

          The Seller hereby represents, warrants and agrees as of the Settlement
Date as follows:

          (a) The  Seller  has full  power  and  authority  to enter  into  this
Agreement and to consummate  the  Transaction.  This Agreement has been duly and
validly  executed and delivered by the Seller and constitutes  the legal,  valid
and binding obligation of the Seller,  enforceable in accordance with its terms,
except  as  such  enforceability  may  be  limited  by  applicable   bankruptcy,
insolvency,  moratorium,  reorganization  or  similar  laws from time to time in
effect that  affect  creditors'  rights  generally,  and by legal and  equitable
limitations on the availability of specific remedies.

          (b) The  execution,  delivery  and  performance  by the Seller of this
Agreement and consummation by the Seller of the Transaction do not and will not:
(i) violate any decree or judgment of any court or other governmental  authority
applicable  to or binding on the  Seller;  (ii)  violate  any  provision  of any
federal  or  state  statute,  rule  or  regulation  which  is,  to the  Seller's
knowledge,  applicable to the Seller; or (iii) violate any contract to which the
Seller or any of its assets or properties are bound. To the Seller's  knowledge,
no consent or approval of, or filing with, any  governmental  authority or other
person  not  a  party  hereto  is  required  for  the  execution,  delivery  and
performance  by  the  Seller  of  this  Agreement  or  the  consummation  of the
Transaction.

          (c) With respect to the Transaction,  (a) the Seller is the record and
beneficial  owner of the  Shares,  free and clear of any  Encumbrances;  (b) the
Shares to be delivered are not subject to any Transfer Restriction; and (c) upon
the  transfer  of the  Shares to  Purchaser,  Purchaser  will  acquire  good and
marketable  title  thereto  (assuming  that  Purchaser is a bona fide  purchaser
within the meaning of Section  8-302 of the New York Uniform  Commercial  Code),
and will be the legal and beneficial owner of such Shares, free and clear of any
Encumbrances or Transfer Restrictions.

          (d) No  proceedings  relating  to the  Shares are  pending  or, to the
knowledge  of  the  Seller,   threatened   before  any  court,   arbitrator   or
administrative  or governmental  body that would  adversely  affect the Seller's
right to transfer the Shares to the Purchaser.

          (e) The Seller has provided or made  available to the  Purchaser  upon
Purchaser's written request any information and documents  reasonably  requested
by the Purchaser; however, the Seller has not provided any Xmark Information (as
defined in Section 4(d) below) to the Purchaser.

          4. Representations, Warranties and Agreement of the Purchaser.

          The  Purchaser  hereby  represents,  warrants  and  agrees  as of  the
Settlement Date as follows:

          (a) The  Purchaser  is duly  organized,  validly  existing and in good
standing in its jurisdiction of organization.




          (b) The  Purchaser  has full  power and  authority  to enter into this
Agreement  and to  consummate  the  Transaction.  The  execution,  delivery  and
performance of this Agreement by the Purchaser have been duly  authorized by all
necessary   corporate/company/partnership   proceedings   on  the  part  of  the
Purchaser.  This  Agreement has been duly and validly  executed and delivered by
the Purchaser and  constitutes  the legal,  valid and binding  obligation of the
Purchaser,   enforceable   in  accordance   with  its  terms,   except  as  such
enforceability may be limited by applicable bankruptcy,  insolvency, moratorium,
reorganization  or  similar  laws in  effect  that  affect  the  enforcement  of
creditors' rights generally and by equitable  limitations on the availability of
specific remedies.

          (c) The execution,  delivery and  performance by the Purchaser of this
Agreement and  consummation  by the Purchaser of the Transaction do not and will
not:  (i)  violate  any decree or  judgment  of any court or other  governmental
authority applicable to or binding on the Purchaser;  (ii) violate any provision
of any federal or state statute, rule or regulation which is, to the Purchaser's
knowledge,  applicable to the Purchaser; (iii) violate any contract to which the
Purchaser  is a  party  or by  which  the  Purchaser  or any of  its  assets  or
properties  are bound;  or (iv)  violate or conflict  with any  provision of the
charter or by-laws of the Purchaser.  No consent or approval of, or filing with,
any  governmental  authority  or other person not a party hereto is required for
the  execution,  delivery and  performance by the Purchaser of this Agreement or
the consummation of the Transaction.

          (d) The Purchaser is aware that the Seller, Xmark Fund, L.P. and Xmark
Asset Management, LLC (collectively,  the "Xmark Funds") may be in possession of
certain nonpublic information  concerning the Company and the Shares (the "Xmark
Information"), and that the Xmark Funds have agreed with the Company to keep the
Xmark  Information  confidential.  The  Purchaser  acknowledges  that Seller has
advised it that a reasonable  investor  could deem the Xmark  Information  to be
material to an investment  decision,  and that the Xmark Information could be of
an adverse nature to an investor in the Shares. The Purchaser is freely deciding
to purchase the Shares at the agreed-upon price for its own reasons based on the
information it currently possesses,  which it deems sufficient,  notwithstanding
that it may lack  access  to the  Xmark  Information,  to make its  decision  to
participate  in the purchase and sale of the Shares.  The Purchaser does not and
will not  request,  desire  or  require  any of the Xmark  Funds,  now or in the
future,  to disclose any or all of the Xmark Information to the Purchaser or any
of its affiliates, agents or representatives.

          5. Purchaser  Release and Waiver.  The Purchaser  agrees not to pursue
and to release fully any potential suits,  claims,  causes of action,  remedies,
damages and other actions  whatsoever,  at law or in equity,  against any of the
Xmark Funds and their  respective  affiliates,  officers,  directors,  managers,
members,  agents,  employees,  representatives  and assigns,  arising out of the
purchase of the Shares (other than with respect to any claim against  Seller for
a breach of this Agreement) or the nondisclosure of the Xmark Information to the
Purchaser.   The  Purchaser   hereby   acknowledges   receipt  of   satisfactory
consideration for the agreements set forth in this paragraph,  including but not
limited  to the  consummation  of the  purchase  and sale of the  Shares  at the
agreed-upon purchase price. The Purchaser acknowledges and agrees that Seller is
relying on this Section 5 in engaging in the sale  herein,  and would not engage
in the sale of the Shares in the absence of this Section 5.




          6  Conditions   Precedent  to  Obligations   of  the  Purchaser.   The
obligations  of the Purchaser are subject to the  satisfaction  of the following
conditions precedent:

          (a) The  representations and warranties of the Seller contained herein
shall be true and correct as of the Settlement Date.

          (b) The  Seller  shall have  complied  with all of its  covenants  and
agreements  contained herein to be performed by it on or prior to the Settlement
Date.

          (c) The Company shall have removed the legend on the Shares.

          7. Conditions  Precedent to Obligations of the Seller. The obligations
of the  Seller are  subject  to the  satisfaction  of the  following  conditions
precedent:

          (a) The  representations  and  warranties of the  Purchaser  contained
herein shall be true and correct as of the Settlement Date.

          (b) The  Purchaser  shall have  complied with all of its covenants and
agreements  contained herein to be performed by it on or prior to the Settlement
Date.

          (c) The Seller shall have  received the wire  transfer  referred to in
Section 8(c).

          (d) The Company shall have removed the legend on the Shares.

          8. Settlement.

          (a) Settlement of the Transaction  shall take place on the date agreed
upon by the parties as soon as  practicable  following the  satisfaction  of the
conditions  set forth in  Sections 6 and 7 of this  Agreement  (the  "Settlement
Date");  provided,  however, this Agreement shall terminate and be of no further
force and effect if the  Settlement  Date has not  occurred on or prior to March
11, 2005. On the Settlement  Date, the Seller shall deliver to the Purchaser the
Shares  against  payment by the  Purchaser  of the  Purchase  Price.  Subject to
Sections 6 and 7 of this Agreement, the purchase and sale of the Shares shall be
effective as of the Settlement Date.

          (b) The Shares  delivered to the Purchaser  pursuant to this Agreement
shall be free and  clear of all  Encumbrances  and  Transfer  Restrictions.  The
transfer of the Shares to the Purchaser  shall have been registered on the books
of the Issuer and/or any applicable transfer agent. Unless otherwise  instructed
by the Purchaser, the Shares should be delivered to:

          (c) The Purchase  Price shall be paid by wire transfer of  immediately
available funds to the following bank account:




         Chase Manhattan Bank
         ABA #:   021-000-021
         FBO:     Citigroup - Smith Barney Inc
         A/C#:    066-198038
         FFC:     Xmark Fund, Ltd.
         A/C#:    522-43390

          (d) Each of the  Purchaser  and the Seller will,  upon the  reasonable
request  of the  other,  execute  and  deliver  all  other  such  documents  and
instruments reasonably deemed necessary or desirable by the other party to fully
effect the purchases and sales contemplated hereby.

          9. Amendment.  This Agreement may be amended, modified or supplemented
but only in a writing signed by the Seller and the Purchaser.

          10. Notices. Any notice, request,  instruction or other document to be
given  hereunder  by a party  hereto  shall be in writing and shall be deemed to
have been  given,  (a) when  received  if given in  person or by a courier  or a
courier  service  or (b) on the  date  of  transmission  if  sent  by  facsimile
transmission:

          (a) If to the Seller, addressed as follows:

                         Xmark Funds
                         301 Tresser Boulevard, Suite 1320
                         Stamford, CT 06901
                         Attn:  Mitchell Kaye
                         T: 203-653-2500
                         F: 203-653-2501

          (b) If to the Purchaser, addressed as follows:


                         OTATO, L.P., a Grand Cayman limited partnership
                         One Manhattanville Road
                         Purchase, New York  10577
                         Tel: 800 444 9089

          or to such other person or address as a party hereto may designate for
itself by notice given as herein provided.

          11.  Counterparts.  This  Agreement  may be  executed in any number of
counterparts  (including  by  facsimile  transmission),  each of which  shall be
deemed an original,  but all of which together shall constitute one and the same
agreement.

          12.  APPLICABLE LAW. THIS AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED
IN  ACCORDANCE  WITH THE LAWS OF THE  STATE OF NEW YORK  (without  reference  to
choice OF law doctrine).




          13. Expenses.  Except as otherwise  expressly  provided  herein,  each
party hereto will bear its own expenses in connection  with the  purchase(s) and
sale(s) of the Shares contemplated hereby, except that the Seller shall bear all
transfer and issuance taxes imposed on such purchase and sale.

          14. Entire Agreement.  This Agreement constitutes the entire agreement
between  the  parties  hereto  with  respect to the  subject  matter  hereof and
supersedes  all prior  agreements and  understandings  between such parties with
respect to such subject matter.

          15.  Severability.  If any provision of this  Agreement  shall be held
invalid, illegal or unenforceable,  the validity, legality and enforceability of
the other provisions hereof shall not be affected thereby.

          16.  Captions.  The Section  captions  herein are for  convenience  of
reference  only and are not intended to be a part of or to affect the meaning or
interpretation of this Agreement.

          17. Specific  Performance.  The parties acknowledge that money damages
will not be a  sufficient  remedy  for  breach  of this  Agreement  and that the
parties  hereto may obtain  specific  performance  or other  injunctive  relief,
without the necessity of posting a bond or security therefor.


          IN WITNESS  WHEREOF,  the parties hereto have caused this Agreement to
be executed and delivered as of the date first above written.


OTATO, L.P.


By: /s/ Richard Jaffe
Name (Please Print): Richard Jaffe
Title Capacity: Senior Managing Director



XMARK FUND, L.P.

/s/ Mitchell D. Kaye

Name: Mitchell D. Kaye
Title: Chief Investment Officer



                                                                      Exhibit 10

                          SECURITIES PURCHASE AGREEMENT

          This  SECURITIES  PURCHASE  AGREEMENT,  dated as of February  23, 2005
(this  "Agreement"),  is by and between  OTATO,  L.P.,  a Grand  Cayman  limited
partnership  (the  "Purchaser"),  and Xmark Fund,  Ltd, a Cayman Island exempted
company ("Seller").


          WHEREAS,  the Seller owns 50,753 shares (the "Shares") of Common Stock
(the "Common  Stock") of AeroGen  Inc.  (the  "Issuer"),  which shares of Common
Stock  are  subject  to  a  currently  effective   registration  statement  (the
"Registration Statement"); and

          WHEREAS,  the Seller wishes to sell the Shares to the  Purchaser,  and
the Purchaser is willing to purchase the Shares from the Seller.

          NOW,  THEREFORE,  in consideration of the foregoing and the covenants,
agreements  and  warranties  contained  herein,  the  sufficiency  of  which  as
consideration is hereby acknowledged, the parties agree as follows:

          1. Definitions.  When used herein,  the following terms shall have the
indicated meanings:

          "Encumbrance"  means  any  pledge,  hypothecation,  assignment,  lien,
restriction,  charge, claim, security interest, option, preference,  priority or
other preferential arrangement of any kind or nature whatsoever.

          "Transfer  Restriction"  means,  with respect to any security or other
property,  any condition to or  restriction on the ability of the holder thereof
to sell,  assign or otherwise  transfer  such  security or other  property or to
enforce the provisions  thereof or of any document related thereto,  whether set
forth in such  security  or other  property  itself or in any  document  related
thereto or arising by  operation of law,  including,  without  limitation,  such
conditions or restrictions  arising under federal,  state or foreign  securities
laws or under contract.

          2. Sale and Purchase.

          (a) On the  Settlement  Date,  the Seller shall sell to the Purchaser,
and the Purchaser shall purchase from the Seller (the "Transaction"), the Shares
for an aggregate purchase price (the "Purchase Price") of $91,355.40 in cash.

          (b) On the Settlement Date, the Seller shall deliver to the Purchaser,
at the address set forth in Section 8 hereof, the Shares, duly endorsed.




          (c) On the Settlement  Date, the Purchaser shall deliver to the Seller
the  Purchase  Price by wire  transfer  of  immediately  available  funds to the
account designed in writing by the Seller.


          3. Representations, Warranties and Agreements of the Seller.

          The Seller hereby represents, warrants and agrees as of the Settlement
Date as follows:

          (a) The  Seller  has full  power  and  authority  to enter  into  this
Agreement and to consummate  the  Transaction.  This Agreement has been duly and
validly  executed and delivered by the Seller and constitutes  the legal,  valid
and binding obligation of the Seller,  enforceable in accordance with its terms,
except  as  such  enforceability  may  be  limited  by  applicable   bankruptcy,
insolvency,  moratorium,  reorganization  or  similar  laws from time to time in
effect that  affect  creditors'  rights  generally,  and by legal and  equitable
limitations on the availability of specific remedies.

          (b) The  execution,  delivery  and  performance  by the Seller of this
Agreement and consummation by the Seller of the Transaction do not and will not:
(i) violate any decree or judgment of any court or other governmental  authority
applicable  to or binding on the  Seller;  (ii)  violate  any  provision  of any
federal  or  state  statute,  rule  or  regulation  which  is,  to the  Seller's
knowledge,  applicable to the Seller; or (iii) violate any contract to which the
Seller or any of its assets or properties are bound. To the Seller's  knowledge,
no consent or approval of, or filing with, any  governmental  authority or other
person  not  a  party  hereto  is  required  for  the  execution,  delivery  and
performance  by  the  Seller  of  this  Agreement  or  the  consummation  of the
Transaction.

          (c) With respect to the Transaction,  (a) the Seller is the record and
beneficial  owner of the  Shares,  free and clear of any  Encumbrances;  (b) the
Shares to be delivered are not subject to any Transfer Restriction; and (c) upon
the  transfer  of the  Shares to  Purchaser,  Purchaser  will  acquire  good and
marketable  title  thereto  (assuming  that  Purchaser is a bona fide  purchaser
within the meaning of Section  8-302 of the New York Uniform  Commercial  Code),
and will be the legal and beneficial owner of such Shares, free and clear of any
Encumbrances or Transfer Restrictions.

          (d) No  proceedings  relating  to the  Shares are  pending  or, to the
knowledge  of  the  Seller,   threatened   before  any  court,   arbitrator   or
administrative  or governmental  body that would  adversely  affect the Seller's
right to transfer the Shares to the Purchaser.

          (e) The Seller has provided or made  available to the  Purchaser  upon
Purchaser's written request any information and documents  reasonably  requested
by the Purchaser; however, the Seller has not provided any Xmark Information (as
defined in Section 4(d) below) to the Purchaser.




          4. Representations, Warranties and Agreement of the Purchaser.

          The  Purchaser  hereby  represents,  warrants  and  agrees  as of  the
Settlement Date as follows:

          (a) The  Purchaser  is duly  organized,  validly  existing and in good
standing in its jurisdiction of organization.

          (b) The  Purchaser  has full  power and  authority  to enter into this
Agreement  and to  consummate  the  Transaction.  The  execution,  delivery  and
performance of this Agreement by the Purchaser have been duly  authorized by all
necessary   corporate/company/partnership   proceedings   on  the  part  of  the
Purchaser.  This  Agreement has been duly and validly  executed and delivered by
the Purchaser and  constitutes  the legal,  valid and binding  obligation of the
Purchaser,   enforceable   in  accordance   with  its  terms,   except  as  such
enforceability may be limited by applicable bankruptcy,  insolvency, moratorium,
reorganization  or  similar  laws in  effect  that  affect  the  enforcement  of
creditors' rights generally and by equitable  limitations on the availability of
specific remedies.

          (c) The execution,  delivery and  performance by the Purchaser of this
Agreement and  consummation  by the Purchaser of the Transaction do not and will
not:  (i)  violate  any decree or  judgment  of any court or other  governmental
authority applicable to or binding on the Purchaser;  (ii) violate any provision
of any federal or state statute, rule or regulation which is, to the Purchaser's
knowledge,  applicable to the Purchaser; (iii) violate any contract to which the
Purchaser  is a  party  or by  which  the  Purchaser  or any of  its  assets  or
properties  are bound;  or (iv)  violate or conflict  with any  provision of the
charter or by-laws of the Purchaser.  No consent or approval of, or filing with,
any  governmental  authority  or other person not a party hereto is required for
the  execution,  delivery and  performance by the Purchaser of this Agreement or
the consummation of the Transaction.

          (d) The Purchaser is aware that the Seller, Xmark Fund, L.P. and Xmark
Asset Management, LLC (collectively,  the "Xmark Funds") may be in possession of
certain nonpublic information  concerning the Company and the Shares (the "Xmark
Information"), and that the Xmark Funds have agreed with the Company to keep the
Xmark  Information  confidential.  The  Purchaser  acknowledges  that Seller has
advised it that a reasonable  investor  could deem the Xmark  Information  to be
material to an investment  decision,  and that the Xmark Information could be of
an adverse nature to an investor in the Shares. The Purchaser is freely deciding
to purchase the Shares at the agreed-upon price for its own reasons based on the
information it currently possesses,  which it deems sufficient,  notwithstanding
that it may lack  access  to the  Xmark  Information,  to make its  decision  to
participate  in the purchase and sale of the Shares.  The Purchaser does not and
will not  request,  desire  or  require  any of the Xmark  Funds,  now or in the
future,  to disclose any or all of the Xmark Information to the Purchaser or any
of its affiliates, agents or representatives.




          5. Purchaser  Release and Waiver.  The Purchaser  agrees not to pursue
and to release fully any potential suits,  claims,  causes of action,  remedies,
damages and other actions  whatsoever,  at law or in equity,  against any of the
Xmark Funds and their  respective  affiliates,  officers,  directors,  managers,
members,  agents,  employees,  representatives  and assigns,  arising out of the
purchase of the Shares (other than with respect to any claim against  Seller for
a breach of this Agreement) or the nondisclosure of the Xmark Information to the
Purchaser.   The  Purchaser   hereby   acknowledges   receipt  of   satisfactory
consideration for the agreements set forth in this paragraph,  including but not
limited  to the  consummation  of the  purchase  and sale of the  Shares  at the
agreed-upon purchase price. The Purchaser acknowledges and agrees that Seller is
relying on this Section 5 in engaging in the sale  herein,  and would not engage
in the sale of the Shares in the absence of this Section 5.

          6  Conditions   Precedent  to  Obligations   of  the  Purchaser.   The
obligations  of the Purchaser are subject to the  satisfaction  of the following
conditions precedent:

          (a) The  representations and warranties of the Seller contained herein
shall be true and correct as of the Settlement Date.

          (b) The  Seller  shall have  complied  with all of its  covenants  and
agreements  contained herein to be performed by it on or prior to the Settlement
Date.

          (c) The Company shall have removed the legend on the Shares.

          7. Conditions  Precedent to Obligations of the Seller. The obligations
of the  Seller are  subject  to the  satisfaction  of the  following  conditions
precedent:

          (a) The  representations  and  warranties of the  Purchaser  contained
herein shall be true and correct as of the Settlement Date.

          (b) The  Purchaser  shall have  complied with all of its covenants and
agreements  contained herein to be performed by it on or prior to the Settlement
Date.

          (c) The Seller shall have  received the wire  transfer  referred to in
Section 8(c).

          (d) The Company shall have removed the legend on the Shares.

          8. Settlement.

          (a) Settlement of the Transaction  shall take place on the date agreed
upon by the parties as soon as  practicable  following the  satisfaction  of the
conditions  set forth in  Sections 6 and 7 of this  Agreement  (the  "Settlement
Date");  provided,  however, this Agreement shall terminate and be of no further
force and effect if the  Settlement  Date has not  occurred on or prior to March
11, 2005. On the Settlement  Date, the Seller shall deliver to the Purchaser the
Shares  against  payment by the  Purchaser  of the  Purchase  Price.  Subject to
Sections 6 and 7 of this Agreement, the purchase and sale of the Shares shall be
effective as of the Settlement Date.




          (b) The Shares  delivered to the Purchaser  pursuant to this Agreement
shall be free and  clear of all  Encumbrances  and  Transfer  Restrictions.  The
transfer of the Shares to the Purchaser  shall have been registered on the books
of the Issuer and/or any applicable transfer agent. Unless otherwise  instructed
by the Purchaser, the Shares should be delivered to:

          (c) The Purchase  Price shall be paid by wire transfer of  immediately
available funds to the following bank account:

         Chase Manhattan Bank
         ABA #:   021-000-021
         FBO:     Citigroup - Smith Barney Inc
         A/C#:    066-198038
         FFC:     Xmark Fund, Ltd.
         A/C#:    522-43390

          (d) Each of the  Purchaser  and the Seller will,  upon the  reasonable
request  of the  other,  execute  and  deliver  all  other  such  documents  and
instruments reasonably deemed necessary or desirable by the other party to fully
effect the purchases and sales contemplated hereby.

          9. Amendment.  This Agreement may be amended, modified or supplemented
but only in a writing signed by the Seller and the Purchaser.

          10. Notices. Any notice, request,  instruction or other document to be
given  hereunder  by a party  hereto  shall be in writing and shall be deemed to
have been  given,  (a) when  received  if given in  person or by a courier  or a
courier  service  or (b) on the  date  of  transmission  if  sent  by  facsimile
transmission:

          (a) If to the Seller, addressed as follows:

                         Xmark Funds
                         301 Tresser Boulevard, Suite 1320
                         Stamford, CT 06901
                         Attn:  Mitchell Kaye
                         T: 203-653-2500
                         F: 203-653-2501

          (b) If to the Purchaser, addressed as follows:


                         OTATO, L.P., a Grand Cayman limited partnership
                         One Manhattanville Road
                         Purchase, New York  10577
                         Tel: 800 444 9089

          or to such other person or address as a party hereto may designate for
itself by notice given as herein provided.




          11.  Counterparts.  This  Agreement  may be  executed in any number of
counterparts  (including  by  facsimile  transmission),  each of which  shall be
deemed an original,  but all of which together shall constitute one and the same
agreement.

          12.  APPLICABLE LAW. THIS AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED
IN  ACCORDANCE  WITH THE LAWS OF THE  STATE OF NEW YORK  (without  reference  to
choice OF law doctrine).

          13. Expenses.  Except as otherwise  expressly  provided  herein,  each
party hereto will bear its own expenses in connection  with the  purchase(s) and
sale(s) of the Shares contemplated hereby, except that the Seller shall bear all
transfer and issuance taxes imposed on such purchase and sale.

          14. Entire Agreement.  This Agreement constitutes the entire agreement
between  the  parties  hereto  with  respect to the  subject  matter  hereof and
supersedes  all prior  agreements and  understandings  between such parties with
respect to such subject matter.

          15.  Severability.  If any provision of this  Agreement  shall be held
invalid, illegal or unenforceable,  the validity, legality and enforceability of
the other provisions hereof shall not be affected thereby.

          16.  Captions.  The Section  captions  herein are for  convenience  of
reference  only and are not intended to be a part of or to affect the meaning or
interpretation of this Agreement.

          17. Specific  Performance.  The parties acknowledge that money damages
will not be a  sufficient  remedy  for  breach  of this  Agreement  and that the
parties  hereto may obtain  specific  performance  or other  injunctive  relief,
without the necessity of posting a bond or security therefor.


          IN WITNESS  WHEREOF,  the parties hereto have caused this Agreement to
be executed and delivered as of the date first above written.


OTATO, L.P.


By: /s/ Richard Jaffe
Name (Please Print): Richard Jaffe
Title Capacity: Senior Managing Director



XMARK FUND, LTD.


/s/ Mitchell D. Kaye

Name: Mitchell D. Kaye
Title: Chief Investment Officer