<SUBMISSION>
<ACCESSION-NUMBER>0000950005-01-000121
<TYPE>SC 13G
<PUBLIC-DOCUMENT-COUNT>1
<FILING-DATE>20010213
<SUBJECT-COMPANY>
<COMPANY-DATA>
<CONFORMED-NAME>AEROGEN INC
<CIK>0001039160
<ASSIGNED-SIC>3845
<IRS-NUMBER>330488580
<STATE-OF-INCORPORATION>DE
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<FILING-VALUES>
<FORM-TYPE>SC 13G
<ACT>34
<FILE-NUMBER>005-60561
<FILM-NUMBER>1536063
</FILING-VALUES>
<BUSINESS-ADDRESS>
<STREET1>1310 CORONADO DR
<CITY>SANTA CLARA
<STATE>CA
<ZIP>95054
<PHONE>4085432400
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>1310 ORLEANS DRIVE
<CITY>SUNNYVALE
<STATE>CA
<ZIP>94089
</MAIL-ADDRESS>
</SUBJECT-COMPANY>
<FILED-BY>
<COMPANY-DATA>
<CONFORMED-NAME>U S VENTURE PARTNERS IV L P
<CIK>0001030241
<ASSIGNED-SIC>
</COMPANY-DATA>
<FILING-VALUES>
<FORM-TYPE>SC 13G
</FILING-VALUES>
<BUSINESS-ADDRESS>
<STREET1>2180 SAND HILL ROAD SUITE 300
<CITY>MENLO PARK
<STATE>CA
<ZIP>94025
<PHONE>4158549080
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>2180 SAND HILL ROAD
<STREET2>SUITE 300
<CITY>MENLO PARK
<STATE>CA
<ZIP>94025
</MAIL-ADDRESS>
</FILED-BY>
<DOCUMENT>
<TYPE>SC 13G
<SEQUENCE>1
<FILENAME>0001.txt
<DESCRIPTION>FORM SC 13G
<TEXT>



                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  Schedule 13G
                                 (Rule 13d-102)

  INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO RULES 13d-1 (b),
         (c) AND (d) AND AMENDMENTS THERETO FILED PURSUANT TO 13d-2 (b)
                            (Amendment No._______)*


                                 AeroGen, Inc.
--------------------------------------------------------------------------------
                                (Name of Issuer)

                                  Common Stock
--------------------------------------------------------------------------------
                         (Title of Class of Securities)

                                   007779101
--------------------------------------------------------------------------------
                                 (CUSIP Number)

                               December 31, 2000
--------------------------------------------------------------------------------
            (Date of Event Which Requires Filing of this Statement)

Check the  appropriate box to designate the rule pursuant to which this Schedule
is filed:

        [ ]          Rule 13d-1(b)

        [ ]          Rule 13d-1(c)

        [X]          Rule 13d-1(d)

*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).

                         (Continued on following pages)



                               Page 1 of 18 Pages


<PAGE>



<TABLE>
<CAPTION>
<S>                                                                            <C>
----------------------------------------------------------                     --------------------------------------
CUSIP NO. 007779101                                               13 G                  Page 2 of 18 Pages
----------------------------------------------------------                     --------------------------------------

------------ ---------------------------------------------------------------------------------------------------------

1            NAME OF REPORTING PERSON
             I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)
                      U.S. Venture Partners IV, L.P. ("USVP IV")
------------ ---------------------------------------------------------------------------------------------------------

2            CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                                    (a)  [ ]            (b)  [X]
------------ ---------------------------------------------------------------------------------------------------------

3            SEC USE ONLY
------------ ---------------------------------------------------------------------------------------------------------

4            CITIZENSHIP OR PLACE OF ORGANIZATION
                      Delaware

------------ ---------------------------------------------------------------------------------------------------------
             NUMBER OF
              SHARES                 5        SOLE VOTING POWER
           BENEFICIALLY                       1,674,763 shares, except that Presidio Management Group IV, L.P.
           OWNED BY EACH                      ("PMG IV"), the general partner of USVP IV, may be deemed to have sole
             REPORTING                        voting power with respect to such shares, and William K Bowes, Jr.
              PERSON                          ("Bowes"), Irwin Federman ("Federman"), Steven M. Krausz ("Krausz")
               WITH                           and Philip M. Young ("Young"), the  general partners of PMG IV, may be
                                              deemed to have shared voting power with respect to such shares.
                                     -------- ------------------------------------------------------------------------

                                     6        SHARED VOTING POWER
                                              See response to row 5.
                                     -------- ------------------------------------------------------------------------

                                     7        SOLE DISPOSITIVE POWER
                                              1,674,763 shares, except that PMG IV, the general partner of USVP IV,
                                              may be deemed to have sole dispositive power with respect to such
                                              shares, and Bowes, Federman, Krausz and Young, the general partners
                                              of PMG IV, may be deemed to have shared dispositive power with
                                              respect to such shares.
                                     -------- ------------------------------------------------------------------------

                                     8        SHARED DISPOSITIVE POWER
                                              See response to row 7.
------------------------------------ -------- ------------------------------------------------------------------------

9            AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH
             REPORTING PERSON                                                                       1,674,763
------------ ---------------------------------------------------------------------------------------------------------

10           CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9)
             EXCLUDES CERTAIN SHARES*                                                                [ ]
------------ ---------------------------------------------------------------------------------------------------------

11           PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
                                                                                                    8.64%
------------ ---------------------------------------------------------------------------------------------------------

12           TYPE OF REPORTING PERSON*
                                                                                                      PN
------------ ---------------------------------------------------------------------------------------------------------
<FN>
                                                * SEE INSTRUCTIONS BEFORE FILLING OUT!
</FN>
</TABLE>

<PAGE>



<TABLE>
<CAPTION>
<S>                                                                            <C>
----------------------------------------------------------                     --------------------------------------
CUSIP NO. 007779101                                               13 G                  Page 3 of 18 Pages
----------------------------------------------------------                     --------------------------------------

------------ ---------------------------------------------------------------------------------------------------------

1            NAME OF REPORTING PERSON
             I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)
                       Second Ventures II, L.P. ("SV II")

------------ ---------------------------------------------------------------------------------------------------------

2            CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                                    (a)  [ ]            (b)  [X]
------------ ---------------------------------------------------------------------------------------------------------

3            SEC USE ONLY
------------ ---------------------------------------------------------------------------------------------------------

4            CITIZENSHIP OR PLACE OF ORGANIZATION
                      Cayman Islands

------------ ---------------------------------------------------------------------------------------------------------
             NUMBER OF
              SHARES                 5        SOLE VOTING POWER
           BENEFICIALLY                       203,295 shares,  except that PMG IV, the general partner of SV II, may
          OWNED BY EACH                       be deemed to have sole voting  power with respect to such shares, and
             REPORTING                        Bowes,  Federman,  Krausz and Young, the general partners of PMG IV, may
              PERSON                          be deemed to have shared  voting  power with respect to such shares.
               WITH                  -------- ------------------------------------------------------------------------

                                     6        SHARED VOTING POWER
                                              See response to row 5.
                                     -------- ------------------------------------------------------------------------

                                     7        SOLE DISPOSITIVE POWER
                                              203,295 shares, except that PMG IV, the general partner of SV II, may
                                              be deemed to have sole dispositive power with respect to such shares,
                                              and Bowes, Federman, Krausz and Young, the general partners of
                                              PMG IV, may be deemed to have shared dispositive power with respect
                                              to such shares.
                                     -------- ------------------------------------------------------------------------

                                     8        SHARED DISPOSITIVE POWER
                                              See response to row 7.
------------------------------------ -------- ------------------------------------------------------------------------

9            AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH
             REPORTING PERSON                                                                       203,295
------------ ---------------------------------------------------------------------------------------------------------

10           CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9)
             EXCLUDES CERTAIN SHARES*                                                                [ ]
------------ ---------------------------------------------------------------------------------------------------------

11           PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
                                                                                                    1.05 %
------------ ---------------------------------------------------------------------------------------------------------

12           TYPE OF REPORTING PERSON*
                                                                                                      PN
------------ ---------------------------------------------------------------------------------------------------------
<FN>

                                                * SEE INSTRUCTIONS BEFORE FILLING OUT!
</FN>
</TABLE>



<PAGE>


<TABLE>
<CAPTION>
<S>                                                                            <C>
----------------------------------------------------------                     --------------------------------------
CUSIP NO. 007779101                                               13 G                  Page 4 of 18 Pages
----------------------------------------------------------                     --------------------------------------

------------ ---------------------------------------------------------------------------------------------------------

1            NAME OF REPORTING PERSON
             I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)
                      USVP Entrepreneur Partners II, L.P. ("UEP II")
------------ ---------------------------------------------------------------------------------------------------------

2            CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                                    (a)  [ ]            (b)  [X]
------------ ---------------------------------------------------------------------------------------------------------

3            SEC USE ONLY
------------ ---------------------------------------------------------------------------------------------------------

4            CITIZENSHIP OR PLACE OF ORGANIZATION
                      Delaware
------------ ---------------------------------------------------------------------------------------------------------
             NUMBER OF
              SHARES                 5        SOLE VOTING POWER
           BENEFICIALLY                       58,084 shares,  except that PMG IV, the general partner of UEP II, may
           OWNED BY EACH                      be deemed to have sole voting power with respect to such shares, and
             REPORTING                        Bowes,  Federman,  Krausz and Young, the general partners  of PMG IV, may
              PERSON                          be deemed to have shared  voting  power with respect to such shares.
               WITH                  -------- ------------------------------------------------------------------------

                                     6        SHARED VOTING POWER
                                              See response to row 5.
                                     -------- ------------------------------------------------------------------------

                                     7        SOLE DISPOSITIVE POWER
                                              58,084 shares, except that PMG IV, the general partner of UEP II, may
                                              be deemed to have sole dispositive power with respect to such shares,
                                              and Bowes, Federman, Krausz and Young, the general partners of
                                              PMG IV, may be deemed to have shared dispositive power with respect
                                              to such shares.
                                     -------- ------------------------------------------------------------------------

                                     8        SHARED DISPOSITIVE POWER
                                              See response to row 7.
------------------------------------ -------- ------------------------------------------------------------------------

9            AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH
             REPORTING PERSON                                                                       58,084
------------ ---------------------------------------------------------------------------------------------------------

10           CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9)
             EXCLUDES CERTAIN SHARES*                                                               [ ]
------------ ---------------------------------------------------------------------------------------------------------

11           PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
                                                                                                    0.30%
------------ ---------------------------------------------------------------------------------------------------------

12           TYPE OF REPORTING PERSON*
                                                                                                      PN
------------ ---------------------------------------------------------------------------------------------------------
<FN>

                                                * SEE INSTRUCTIONS BEFORE FILLING OUT!
</FN>
</TABLE>



<PAGE>


<TABLE>
<CAPTION>
<S>                                                                            <C>
----------------------------------------------------------                     --------------------------------------
CUSIP NO. 007779101                                               13 G                  Page 5 of 18 Pages
----------------------------------------------------------                     --------------------------------------

------------ ---------------------------------------------------------------------------------------------------------

1            NAME OF REPORTING PERSON
             I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)
                      Presidio Management Group IV, L.P. ("PMG IV")
------------ ---------------------------------------------------------------------------------------------------------

2            CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                                    (a)  [ ]            (b)  [X]
------------ ---------------------------------------------------------------------------------------------------------

3            SEC USE ONLY
------------ ---------------------------------------------------------------------------------------------------------

4            CITIZENSHIP OR PLACE OF ORGANIZATION
                      Delaware
------------------------------------ -------- ------------------------------------------------------------------------
             NUMBER OF                        SOLE VOTING POWER
              SHARES                 5        1,936,142 shares, of which 1,674,763 are directly owned by USVP IV,
           BENEFICIALLY                       203,295 are directly owned by SV II and 58,084 are directly owned by
           OWNED BY EACH                      UEP II.  PMG IV is the general partner of USVP IV, SV II and UEP II,
             REPORTING                        and may be deemed to have sole voting power with respect to such
              PERSON                          shares, and Bowes, Federman, Krausz and Young, the general partners of
               WITH                           PMG IV, may be deemed to have shared voting power with respect to such
                                              shares.
                                     -------- ------------------------------------------------------------------------

                                     6        See response to row 5.
                                     -------- ------------------------------------------------------------------------

                                     7        SOLE DISPOSITIVE POWER
                                              1,936,142 shares, of which 1,674,763 are directly owned by USVP IV,
                                              203,295 are directly owned by SV II and 58,084 are directly owned by
                                              UEP II. PMG IV is the general partner of USVP IV, SV II and UEP II,
                                              and may be deemed to have sole dispositive power with respect to such
                                              shares, and Bowes, Federman, Krausz and Young, the general partners
                                              of PMG IV, may be deemed to have shared dispositive power with
                                              respect to such shares.
                                     -------- ------------------------------------------------------------------------

                                     8        SHARED DISPOSITIVE POWER
                                              See response to row 7.
------------------------------------ -------- ------------------------------------------------------------------------

9            AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH
             REPORTING PERSON                                                                       1,936,142
------------ ---------------------------------------------------------------------------------------------------------

10           CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9)
             EXCLUDES CERTAIN SHARES*                                                                [ ]
------------ ---------------------------------------------------------------------------------------------------------

11           PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
                                                                                                    9.99%
------------ ---------------------------------------------------------------------------------------------------------

12           TYPE OF REPORTING PERSON*
                                                                                                      PN
------------ ---------------------------------------------------------------------------------------------------------
<FN>

                                                * SEE INSTRUCTIONS BEFORE FILLING OUT!
</FN>
</TABLE>



<PAGE>


<TABLE>
<CAPTION>
<S>                                                                            <C>
----------------------------------------------------------                     --------------------------------------
CUSIP NO. 007779101                                               13 G                  Page 6 of 18 Pages
----------------------------------------------------------                     --------------------------------------

------------ ---------------------------------------------------------------------------------------------------------

1            NAME OF REPORTING PERSON
             I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)
                       William K. Bowes, Jr. ("Bowes")
------------ ---------------------------------------------------------------------------------------------------------

2            CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                                    (a)  [ ]            (b)  [X]
------------ ---------------------------------------------------------------------------------------------------------

3            SEC USE ONLY
------------ ---------------------------------------------------------------------------------------------------------

4            CITIZENSHIP OR PLACE OF ORGANIZATION
                      U.S. Citizen

------------ ---------------------------------------------------------------------------------------------------------
             NUMBER OF
              SHARES                 5        SOLE VOTING POWER
           BENEFICIALLY                       0 shares.
           OWNED BY EACH             -------- ------------------------------------------------------------------------
             REPORTING
              PERSON                 6        SHARED VOTING POWER
               WITH                           1,936,142 shares, of which 1,674,763 are directly owned by USVP IV,
                                              203,295 are directly owned by SV II and 58,084 are directly owned by
                                              UEP II. Bowes is a general partner of PMG IV, the general partner of
                                              USVP IV, SV II and UEP II, and may be deemed to have shared voting
                                              power with respect to such shares.
                                     -------- ------------------------------------------------------------------------

                                     7        SOLE DISPOSITIVE POWER
                                              0 shares.
                                     -------- ------------------------------------------------------------------------

                                     8        SHARED DISPOSITIVE POWER
                                              1,936,142 shares, of which 1,674,763 are directly owned by USVP IV,
                                              203,295 are directly owned by SV II and 58,084 are directly owned by
                                              UEP II. Bowes is a general partner of PMG IV, the general partner of
                                              USVP IV, SV II and UEP II, and may be deemed to have shared
                                              dispositive power with respect to such shares.
------------ ---------------------------------------------------------------------------------------------------------

9            AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH
             REPORTING PERSON                                                                       1,936,142
------------ ---------------------------------------------------------------------------------------------------------

10           CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9)
             EXCLUDES CERTAIN SHARES*                                                                 [ ]
------------ ---------------------------------------------------------------------------------------------------------

11           PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
                                                                                                    9.99%
------------ ---------------------------------------------------------------------------------------------------------

12           TYPE OF REPORTING PERSON*
                                                                                                      IN
------------ ---------------------------------------------------------------------------------------------------------
<FN>

                                                * SEE INSTRUCTIONS BEFORE FILLING OUT!
</FN>
</TABLE>



<PAGE>



<TABLE>
<CAPTION>
<S>                                                                            <C>
----------------------------------------------------------                     --------------------------------------
CUSIP NO. 007779101                                               13 G                  Page 7 of 18 Pages
----------------------------------------------------------                     --------------------------------------

------------ ---------------------------------------------------------------------------------------------------------

1            NAME OF REPORTING PERSON
             I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)
                      Irwin Federman ("Federman")
------------ ---------------------------------------------------------------------------------------------------------

2            CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                                    (a)  [ ]            (b)  [X]
------------ ---------------------------------------------------------------------------------------------------------

3            SEC USE ONLY
------------ ---------------------------------------------------------------------------------------------------------

4            CITIZENSHIP OR PLACE OF ORGANIZATION
                      U.S. Citizen
------------------------------------ -------- ------------------------------------------------------------------------
             NUMBER OF
              SHARES                 5        SOLE VOTING POWER
           BENEFICIALLY                       0 shares.
           OWNED BY EACH             -------- ------------------------------------------------------------------------
             REPORTING
              PERSON                 6        SHARED VOTING POWER
               WITH                           1,936,142 shares, of which 1,674,763 are directly owned by USVP IV,
                                              203,295 are directly owned by SV II and 58,084 are directly owned by
                                              UEP II. Federman is a general partner of PMG IV, the general partner
                                              of USVP IV, SV II and UEP II, and may be deemed to have shared voting
                                              power with respect to such shares.
                                     -------- ------------------------------------------------------------------------

                                     7        SOLE DISPOSITIVE POWER
                                              0 shares.
                                     -------- ------------------------------------------------------------------------

                                     8        SHARED DISPOSITIVE POWER
                                              1,936,142 shares, of which 1,674,763 are directly owned by USVP IV,
                                              203,295 are directly owned by SV II and 58,084 are directly owned by
                                              UEP II. Federman is a general partner of PMG IV, the general partner
                                              of USVP IV, SV II and UEP II, and may be deemed to have shared
                                              dispositive power with respect to such shares.
------------ ---------------------------------------------------------------------------------------------------------

9            AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH
             REPORTING PERSON                                                                       1,936,142
------------ ---------------------------------------------------------------------------------------------------------

10           CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9)
             EXCLUDES CERTAIN SHARES*                                                                [ ]
------------ ---------------------------------------------------------------------------------------------------------

11           PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
                                                                                                    9.99%
------------ ---------------------------------------------------------------------------------------------------------

12           TYPE OF REPORTING PERSON*
                                                                                                      IN
------------ ---------------------------------------------------------------------------------------------------------
<FN>

                                                * SEE INSTRUCTIONS BEFORE FILLING OUT!

</FN>
</TABLE>


<PAGE>

<TABLE>
<CAPTION>
<S>                                                                            <C>
---------------------------------------------------------                     --------------------------------------
CUSIP NO. 007779101                                               13 G                  Page 8 of 18 Pages
----------------------------------------------------------                     --------------------------------------

------------ ---------------------------------------------------------------------------------------------------------

1            NAME OF REPORTING PERSON
             I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)
                      Steven M. Krausz ("Krausz")
------------ ---------------------------------------------------------------------------------------------------------

2            CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                                    (a)  [ ]            (b)  [X]
------------ ---------------------------------------------------------------------------------------------------------

3            SEC USE ONLY
------------ ---------------------------------------------------------------------------------------------------------

4            CITIZENSHIP OR PLACE OF ORGANIZATION
                      U.S. Citizen
------------ ---------------------------------------------------------------------------------------------------------
             NUMBER OF
              SHARES                 5        SOLE VOTING POWER
           BENEFICIALLY                       0 shares.
           OWNED BY EACH             -------- ------------------------------------------------------------------------
             REPORTING
              PERSON                 6        SHARED VOTING POWER
               WITH                           1,936,142 shares, of which 1,674,763 are directly owned by USVP IV,
                                              203,295 are directly owned by SV II and 58,084 are directly owned by
                                              UEP II. Krausz is a general partner of PMG IV, the general partner of
                                              USVP IV, SV II and UEP II, and may be deemed to have shared voting
                                              power with respect to such shares.
                                     -------- ------------------------------------------------------------------------

                                     7        SOLE DISPOSITIVE POWER
                                              0 shares.
                                     -------- ------------------------------------------------------------------------

                                     8        SHARED DISPOSITIVE POWER
                                              1,936,142 shares, of which 1,674,763 are directly owned by USVP IV,
                                              203,295 are directly owned by SV II and 58,084 are directly owned by
                                              UEP II. Krausz is a general partner of PMG IV, the general partner of
                                              USVP IV, SV II and UEP II, and may be deemed to have shared
                                              dispositive power with respect to such shares.
------------ ---------------------------------------------------------------------------------------------------------

9            AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH
             REPORTING PERSON                                                                       1,936,142
------------ ---------------------------------------------------------------------------------------------------------

10           CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9)
             EXCLUDES CERTAIN SHARES*                                                               [ ]
------------ ---------------------------------------------------------------------------------------------------------

11           PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
                                                                                                    9.99%
------------ ---------------------------------------------------------------------------------------------------------

12           TYPE OF REPORTING PERSON*
                                                                                                      IN
------------ ---------------------------------------------------------------------------------------------------------
<FN>

                                                 *SEE INSTRUCTIONS BEFORE FILLING OUT!
</FN>
</TABLE>


<PAGE>


<TABLE>
<CAPTION>
<S>                                                                            <C>
----------------------------------------------------------                     --------------------------------------
CUSIP NO. 007779101                                               13 G                  Page 9 of 18 Pages
----------------------------------------------------------                     --------------------------------------

------------ ---------------------------------------------------------------------------------------------------------

1            NAME OF REPORTING PERSON
             I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)
                      Philip M. Young ("Young")
------------ ---------------------------------------------------------------------------------------------------------

2            CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                                    (a)  [ ]            (b)  [X]
------------ ---------------------------------------------------------------------------------------------------------

3            SEC USE ONLY
------------ ---------------------------------------------------------------------------------------------------------

4            CITIZENSHIP OR PLACE OF ORGANIZATION
                      U.S. Citizen

------------------------------------ -------- ------------------------------------------------------------------------
             NUMBER OF
              SHARES                 5        SOLE VOTING POWER
           BENEFICIALLY                       0 shares.
           OWNED BY EACH             -------- ------------------------------------------------------------------------
             REPORTING
              PERSON                 6        SHARED VOTING POWER
               WITH                           1,936,142 shares, of which 1,674,763 are directly owned by USVP IV,
                                              203,295 are directly owned by SV II and 58,084 are directly owned by
                                              UEP II. Young is a general partner of PMG IV, the general partner of
                                              USVP IV, SV II and UEP II, and may be deemed to have shared voting
                                              power with respect to such shares.
                                     -------- ------------------------------------------------------------------------

                                     7        SOLE DISPOSITIVE POWER
                                              0 shares.
                                     -------- ------------------------------------------------------------------------

                                     8        SHARED DISPOSITIVE POWER
                                              1,936,142 shares, of which 1,674,763 are directly owned by USVP IV,
                                              203,295 are directly owned by SV II and 58,084 are directly owned by
                                              UEP II. Young is a general partner of PMG IV, the general partner of
                                              USVP IV, SV II and UEP II, and may be deemed to have shared
                                              dispositive power with respect to such shares.
------------ ---------------------------------------------------------------------------------------------------------

9            AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH
             REPORTING PERSON                                                                       1,936,142
------------ ---------------------------------------------------------------------------------------------------------

10           CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9)
             EXCLUDES CERTAIN SHARES*                                                               [ ]
------------ ---------------------------------------------------------------------------------------------------------

11           PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
                                                                                                    9.99%
------------ ---------------------------------------------------------------------------------------------------------

12           TYPE OF REPORTING PERSON*
                                                                                                      IN
------------ ---------------------------------------------------------------------------------------------------------
<FN>

                                                * SEE INSTRUCTIONS BEFORE FILLING OUT!
</FN>
</TABLE>


<PAGE>

<TABLE>
<CAPTION>
<S>               <C>
                                                                                                                 Page 10 of 18 Pages


ITEM 1(a).        NAME OF ISSUER:
                  ---------------

                  AeroGen, Inc.

ITEM 1(b).        ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES:
                  ------------------------------------------------

                  1310 Orleans Drive
                  Sunnyvale, California 94089

ITEM 2(a).        NAME OF PERSON FILING:
                  ----------------------

                  This statement is filed by U.S. Venture Partners IV, L.P. ("USVP IV"), Second Ventures II, L.P.
                  ("SV II"), USVP Entrepreneur Partners II, L.P. ("UEP II"), Presidio Management Group IV, L.P.
                  ("PMG IV"), William K. Bowes, Jr. ("Bowes"), Irwin Federman ("Federman"), Steven M. Krausz
                  ("Krausz") and Philip M. Young ("Young"). The foregoing entities and individuals are collectively
                  referred to as the "Reporting Persons".

                  PMG IV is the general partner of USVP IV, SV II and UEP II, and may be deemed to have sole power
                  to vote and sole power to dispose of shares of the issuer directly owned by USVP IV, SV II and
                  UEP II. Bowes, Federman, Krausz and Young are the general partners of PMG IV, and may be deemed
                  to have shared power to vote and shared power to dispose of the shares of issuer directly owned
                  by USVP IV, SV II and UEP II.

ITEM 2(b).        ADDRESS OF PRINCIPAL BUSINESS OFFICE, OR, IF NONE, RESIDENCE:
                  -------------------------------------------------------------

                  The address of the principal business office for each of the Reporting Persons is:

                  U.S. Venture Partners
                  2180 Sand Hill Road, Suite 300
                  Menlo Park, CA  94025

ITEM 2(c)         CITIZENSHIP:
                  ------------

                  USVP IV, UEP II, and PMG IV are Delaware limited partnerships, SV II is a Cayman Islands limited
                  partnership and Bowes, Federman, Krausz and Young are United States citizens.

ITEM 2(d).        TITLE OF CLASS OF SECURITIES:
                  -----------------------------

                  Common Stock

ITEM 2(e).        CUSIP NUMBER:
                  -------------

                  CUSIP # 007779101

ITEM 3.           Not Applicable


</TABLE>


<PAGE>

<TABLE>
<CAPTION>
<S>               <C>

                                                                                                                 Page 11 of 18 Pages

ITEM 4.           OWNERSHIP:
                  ----------

                  The following information with respect to the ownership of the Common Stock of the issuer by the
                  persons filing this Statement is provided as of December 31, 2000:

                           (a)      Amount beneficially owned:
                                    -------------------------

                           See Row 9 of cover page for each Reporting Person.

                           (b)      Percent of Class:
                                    ----------------

                           See Row 11 of cover page for each Reporting Person.

                           (c)      Number of shares as to which such person has:
                                    --------------------------------------------

                                                     (i)      Sole power to vote or to direct the vote:
                                                              ----------------------------------------

                                                              See Row 5 of cover page for each Reporting Person.

                                                     (ii)     Shared power to vote or to direct the vote:
                                                              ------------------------------------------

                                                              See Row 6 of cover page for each Reporting Person.

                                                     (iii)    Sole power to dispose or to direct the disposition of:
                                                              -----------------------------------------------------

                                                              See Row 7 of cover page for each Reporting Person.

                                                     (iv)     Shared power to dispose or to direct the disposition of:
                                                              -------------------------------------------------------

                                                              See Row 8 of cover page for each Reporting Person.

</TABLE>


<PAGE>

<TABLE>
<CAPTION>
<S>               <C>

                                                                                                                 Page 12 of 18 Pages

ITEM 5.           OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS:
                  ---------------------------------------------

                  Not applicable

ITEM 6.           OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON:
                  ---------------------------------------------------------------

                  Under certain circumstances set forth in the limited partnership agreements of USVP IV, SV II,
                  UEP II and PMG IV, the general and limited partners of each of such entities may be deemed to
                  have the right to receive dividends from, or the proceeds from, the sale of shares of the issuer
                  owned by each such entity of which they are a partner.

ITEM 7.           IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE SECURITY BEING REPORTED ON BY THE PARENT
                  HOLDING COMPANY:
                  ----------------

                  Not applicable.

ITEM 8.           IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP:
                  ---------------------------------------------------------

                  Not applicable

ITEM 9.           NOTICE OF DISSOLUTION OF GROUP:
                  ------------------------------

                  Not applicable

ITEM 10.          CERTIFICATION:
                  -------------

                  Not applicable


</TABLE>


<PAGE>

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<CAPTION>
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                                                                                                                 Page 13 of 18 Pages

                                                             SIGNATURES

                  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.

Dated:  February 9, 2001


U.S. Venture Partners IV, L.P.                                   /s/ Michael Maher
By Presidio Management Group IV, L.P.                            ----------------------------------------
Its General Partner                                              Signature

                                                                 Michael Maher
                                                                 Chief Financial Officer/Attorney-In-Fact

Second Ventures II, L.P.                                         /s/ Michael Maher
By Presidio Management Group IV, L.P.                            ----------------------------------------
Its General Partner                                              Signature

                                                                 Michael Maher
                                                                 Chief Financial Officer/Attorney-In-Fact

USVP Entrepreneur Partners II, L.P.                              /s/ Michael Maher
By Presidio Management Group IV, L.P.                            ----------------------------------------
Its General Partner                                              Signature

                                                                 Michael Maher
                                                                 Chief Financial Officer/Attorney-In-Fact

Presidio Management Group IV, L.P.                               /s/ Michael Maher
A Delaware Limited Partnership                                   ----------------------------------------
                                                                 Signature

                                                                 Michael Maher
                                                                 Chief Financial Officer/Attorney-In-Fact

William K. Bowes, Jr.                                            /s/ Michael Maher
                                                                 ----------------------------------------
                                                                 Michael Maher
                                                                 Attorney-In-Fact

Irwin Federman                                                   /s/ Michael Maher
                                                                 ----------------------------------------
                                                                 Michael Maher
                                                                 Attorney-In-Fact


<PAGE>


                                                                                                                 Page 14 of 18 Pages

Steven M. Krausz                                                 /s/ Michael Maher
                                                                 ----------------------------------------
                                                                 Michael Maher
                                                                 Attorney-In-Fact

Philip M. Young                                                  /s/ Michael Maher
                                                                 ----------------------------------------
                                                                 Michael Maher
                                                                 Attorney-In-Fact


</TABLE>


<PAGE>

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<CAPTION>
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                                                                                                                 Page 15 of 18 Pages

                                                             EXHIBIT INDEX

                                                                                              Found on
                                                                                            Sequentially
Exhibit                                                                                     Numbered Page
-------                                                                                     -------------
Exhibit A: Agreement of Joint Filing                                                             16


Exhibit B: Reference to Michael P. Maher as Attorney-In-Fact                                     18




</TABLE>


<PAGE>

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                                                                                                                 Page 16 of 18 Pages


                                                     EXHIBIT A

                                             Agreement of Joint Filing

             The  undersigned  hereby  agree that a single  Schedule 13G (or any
amendment thereto) relating to the Common Stock of AeroGen,  Inc. shall be filed
on behalf of each of the  undersigned  and that this Agreement shall be filed as
an exhibit to such Schedule 13G.

Dated:  February 9, 2001


U.S. Venture Partners IV, L.P.                                   /s/ Michael Maher
By Presidio Management Group IV, L.P.                            ----------------------------------------
Its General Partner                                              Signature

                                                                 Michael Maher
                                                                 Chief Financial Officer/Attorney-In-Fact

Second Ventures II, L.P.                                         /s/ Michael Maher
By Presidio Management Group IV, L.P.                            ----------------------------------------
Its General Partner                                              Signature

                                                                 Michael Maher
                                                                 Chief Financial Officer/Attorney-In-Fact

USVP Entrepreneur Partners II, L.P.                              /s/ Michael Maher
By Presidio Management Group IV, L.P.                            ----------------------------------------
Its General Partner                                              Signature

                                                                 Michael Maher
                                                                 Chief Financial Officer/Attorney-In-Fact

Presidio Management Group IV, L.P.                               /s/ Michael Maher
A Delaware Limited Partnership                                   ----------------------------------------
                                                                 Signature

                                                                 Michael Maher
                                                                 Chief Financial Officer/Attorney-In-Fact

William K. Bowes, Jr.                                            /s/ Michael Maher
                                                                 ----------------------------------------
                                                                 Michael Maher
                                                                 Attorney-In-Fact



<PAGE>


                                                                                                                 Page 17 of 18 Pages
Irwin Federman                                                   /s/ Michael Maher
                                                                 ----------------------------------------
                                                                 Michael Maher
                                                                 Attorney-In-Fact

Steven M. Krausz                                                 /s/ Michael Maher
                                                                 ----------------------------------------
                                                                 Michael Maher
                                                                 Attorney-In-Fact

Philip M. Young                                                  /s/ Michael Maher
                                                                 ----------------------------------------
                                                                 Michael Maher
                                                                 Attorney-In-Fact


</TABLE>


<PAGE>

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<CAPTION>
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                                                                                                                 Page 18 of 18 Pages


                                                              EXHIBIT B

                                           REFERENCE TO MICHAEL MAHER AS ATTORNEY-IN-FACT


                  Michael P. Maher has signed the enclosed documents as Attorney-In-Fact. Note that copies of the applicable Power
of Attorneys are already on file with the appropriate agencies.

</TABLE>
</TEXT>
</DOCUMENT>
</SUBMISSION>
