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                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                  SCHEDULE 13G

                    UNDER THE SECURITIES EXCHANGE ACT OF 1934

                               (AMENDMENT NO. 2)*

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

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

                                    45232710
--------------------------------------------------------------------------------
                                 (CUSIP Number)

                                December 31, 2003
--------------------------------------------------------------------------------
             (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 the
disclosures provided in a prior cover page.

The information required in 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).

                               Page 1 of 15 Pages



------------------                                            ------------------
CUSIP NO. 45232710                      13G                   PAGE 2 OF 15 PAGES
------------------                                            ------------------

--------------------------------------------------------------------------------
1     NAMES OF REPORTING PERSONS
      I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)

            ARCH Venture Fund III, L.P.

--------------------------------------------------------------------------------
2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
                                                                    (a) [ ]
                                                                    (b) [ ]
--------------------------------------------------------------------------------
3     SEC USE ONLY

--------------------------------------------------------------------------------
4     CITIZENSHIP OR PLACE OF ORGANIZATION

            Delaware

--------------------------------------------------------------------------------
                         5    SOLE VOTING POWER

                                    0
       NUMBER OF         -------------------------------------------------------
         SHARES          6    SHARED VOTING POWER
      BENEFICIALLY
        OWNED BY                    3,315,298
          EACH           -------------------------------------------------------
       REPORTING         7    SOLE DISPOSITIVE POWER
         PERSON
          WITH                      0
                         -------------------------------------------------------
                         8    SHARED DISPOSITIVE POWER

                                    3,315,298
--------------------------------------------------------------------------------
9     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

            3,315,298

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

--------------------------------------------------------------------------------
11    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

            10.09%

--------------------------------------------------------------------------------
12    TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

            PN
--------------------------------------------------------------------------------

                      *SEE INSTRUCTIONS BEFORE FILLING OUT!

                               Page 2 of 15 Pages



------------------                                            ------------------
CUSIP NO. 45232710                      13G                   PAGE 3 OF 15 PAGES
------------------                                            ------------------

--------------------------------------------------------------------------------
1     NAMES OF REPORTING PERSONS
      I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)

            ARCH Venture Partners, L.L.C.

--------------------------------------------------------------------------------
2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
                                                                    (a) [ ]
                                                                    (b) [ ]
--------------------------------------------------------------------------------
3     SEC USE ONLY

--------------------------------------------------------------------------------
4     CITIZENSHIP OR PLACE OF ORGANIZATION

            Delaware

--------------------------------------------------------------------------------
                         5    SOLE VOTING POWER

                                    0
                         -------------------------------------------------------
       NUMBER OF         6    SHARED VOTING POWER
         SHARES
      BENEFICIALLY                  3,315,298
        OWNED BY         -------------------------------------------------------
          EACH           7    SOLE DISPOSITIVE POWER
       REPORTING
         PERSON                     0
          WITH           -------------------------------------------------------
                         8    SHARED DISPOSITIVE POWER

                                    3,315,298
--------------------------------------------------------------------------------
9     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

            3,315,298

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

--------------------------------------------------------------------------------
11    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

            10.09%

--------------------------------------------------------------------------------
12    TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

            OO

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

                      *SEE INSTRUCTIONS BEFORE FILLING OUT!

                               Page 3 of 15 Pages



------------------                                            ------------------
CUSIP NO. 45232710                      13G                   PAGE 4 OF 15 PAGES
------------------                                            ------------------

--------------------------------------------------------------------------------
1     NAMES OF REPORTING PERSONS
      I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)

            Steven Lazarus

--------------------------------------------------------------------------------
2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
                                                                    (a) [ ]
                                                                    (b) [ ]
--------------------------------------------------------------------------------
3     SEC USE ONLY

--------------------------------------------------------------------------------
4     CITIZENSHIP OR PLACE OF ORGANIZATION

            U.S.A

--------------------------------------------------------------------------------
                         5    SOLE VOTING POWER

                                    4,625
                         -------------------------------------------------------
       NUMBER OF         6    SHARED VOTING POWER
         SHARES
      BENEFICIALLY                  3,315,298
        OWNED BY         -------------------------------------------------------
          EACH           7    SOLE DISPOSITIVE POWER
       REPORTING
         PERSON                     4,625
          WITH           -------------------------------------------------------
                         8    SHARED DISPOSITIVE POWER

                                    3,315,298
--------------------------------------------------------------------------------
9     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

            3,315,298

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

--------------------------------------------------------------------------------
11    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

            10.11%

--------------------------------------------------------------------------------
12    TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

            IN

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

                      *SEE INSTRUCTIONS BEFORE FILLING OUT!

                               Page 4 of 15 Pages



------------------                                            ------------------
CUSIP NO. 45232710                      13G                   PAGE 5 OF 15 PAGES
------------------                                            ------------------

--------------------------------------------------------------------------------
1     NAMES OF REPORTING PERSONS
      I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)

            Keith Crandell

--------------------------------------------------------------------------------
2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
                                                                    (a) [ ]
                                                                    (b) [ ]
--------------------------------------------------------------------------------
3     SEC USE ONLY

--------------------------------------------------------------------------------
4     CITIZENSHIP OR PLACE OF ORGANIZATION

            U.S.A

--------------------------------------------------------------------------------
                         5    SOLE VOTING POWER

                                    5,395
                         -------------------------------------------------------
       NUMBER OF         6    SHARED VOTING POWER
         SHARES
      BENEFICIALLY                  3,315,298
        OWNED BY         -------------------------------------------------------
          EACH           7    SOLE DISPOSITIVE POWER
       REPORTING
         PERSON                     5,395
          WITH           -------------------------------------------------------
                         8    SHARED DISPOSITIVE POWER

                                    3,315,298
--------------------------------------------------------------------------------
9     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

            3,320,693

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

--------------------------------------------------------------------------------
11    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

            10.11%

--------------------------------------------------------------------------------
12    TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

            IN

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

                      *SEE INSTRUCTIONS BEFORE FILLING OUT!

                               Page 5 of 15 Pages



------------------                                            ------------------
CUSIP NO. 45232710                      13G                   PAGE 6 OF 15 PAGES
------------------                                            ------------------

--------------------------------------------------------------------------------
1     NAMES OF REPORTING PERSONS
      I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)

            Robert Nelsen

--------------------------------------------------------------------------------
2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
                                                                    (a) [ ]
                                                                    (b) [ ]
--------------------------------------------------------------------------------
3     SEC USE ONLY

--------------------------------------------------------------------------------
4     CITIZENSHIP OR PLACE OF ORGANIZATION

            U.S.A

--------------------------------------------------------------------------------
                         5    SOLE VOTING POWER

                                    17,895
                         -------------------------------------------------------
       NUMBER OF         6    SHARED VOTING POWER
         SHARES
      BENEFICIALLY                  3,315,298
        OWNED BY         -------------------------------------------------------
          EACH           7    SOLE DISPOSITIVE POWER
       REPORTING
         PERSON                     17,895
          WITH           -------------------------------------------------------
                         8    SHARED DISPOSITIVE POWER

                                    3,315,298
--------------------------------------------------------------------------------
9     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

            3,333,193

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

--------------------------------------------------------------------------------
11    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

            10.14%

--------------------------------------------------------------------------------
12    TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

            IN

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

                      *SEE INSTRUCTIONS BEFORE FILLING OUT!

                               Page 6 of 15 Pages



------------------                                            ------------------
CUSIP NO. 45232710                      13G                   PAGE 7 OF 15 PAGES
------------------                                            ------------------

--------------------------------------------------------------------------------
1     NAMES OF REPORTING PERSONS
      I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)

            Clinton Bybee

--------------------------------------------------------------------------------
2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
                                                                    (a) [ ]
                                                                    (b) [ ]
--------------------------------------------------------------------------------
3     SEC USE ONLY

--------------------------------------------------------------------------------
4     CITIZENSHIP OR PLACE OF ORGANIZATION

            U.S.A

--------------------------------------------------------------------------------
                         5    SOLE VOTING POWER

                                    5,088
                         -------------------------------------------------------
       NUMBER OF         6    SHARED VOTING POWER
         SHARES
      BENEFICIALLY                  3,315,298
        OWNED BY         -------------------------------------------------------
          EACH           7    SOLE DISPOSITIVE POWER
       REPORTING
         PERSON                     5,088
          WITH           -------------------------------------------------------
                         8    SHARED DISPOSITIVE POWER

                                    3,315,298
--------------------------------------------------------------------------------
9     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

            3,320,386

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

--------------------------------------------------------------------------------
11    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

            10.11%

--------------------------------------------------------------------------------
12    TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

            IN

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

                      *SEE INSTRUCTIONS BEFORE FILLING OUT!

                               Page 7 of 15 Pages



------------------                                            ------------------
CUSIP NO. 45232710                      13G                   PAGE 8 OF 15 PAGES
------------------                                            ------------------

                                  Schedule 13G

Item 1(a).        Name of Issuer: Illumina, Inc. (the "Issuer").

Item 1(b).        Address of Issuer's Principal Executive Offices: 9885 Towne
                  Center Dr., San Diego, CA 92121.

Item 2(a).        Names of Persons Filing: ARCH Venture Fund III, L.P. ("ARCH
                  Venture Fund III"); ARCH Venture Partners, L.L.C. ("AVP LLC")
                  (collectively, the "Reporting Entities" and individually, each
                  a "Reporting Entity") and Steven Lazarus ("Lazarus"), Keith
                  Crandell ("Crandell"), Robert Nelsen ("Nelsen") and Clinton
                  Bybee ("Bybee") (collectively, the "Managing Directors" and
                  individually, each a "Managing Director"). The Reporting
                  Entities and the Managing Directors collectively are referred
                  to as the "Reporting Persons".

Item 2(b).        Address of Principal Business Office or, if None, Residence:
                  8725 W. Higgins Road, Suite 290, Chicago, IL 60631.

Item 2(c).        Citizenship: ARCH Venture Fund III is a limited partnership
                  organized under the laws of the State of Delaware. AVP LLC is
                  a limited liability company organized under the laws of the
                  State of Delaware. Each Managing Director is a US citizen.

Item 2(d).        Title of Class of Securities: Common Stock, $.01 par value
                  (the "Common Stock").

Item 2(e).        CUSIP Number: 45232710

Item 3.           If this statement is filed pursuant to Sections 240.13d-1(b)
                  or 240.13d-2(b) or (c), check whether the person filing is a:

                  Not Applicable.

Item 4.           Ownership.

                  (a)      Amount beneficially owned:

                           ARCH Venture Fund III is the record owner of
                           3,315,298 shares of Common Stock (the "Record
                           Shares") as of December 31, 2003. As the sole general
                           partner of ARCH Venture Fund III, AVP LLC may be
                           deemed to own the Record Shares. As individual
                           general partners or managing directors of AVP LLC,
                           each Managing Director may also be deemed to share
                           the power and direct the disposition and vote of the
                           Record Shares. In addition, as of December 31, 2003,
                           Lazarus is the record holder of 4,625 shares of
                           Common Stock, Bybee is the record holder of 5,088
                           shares of Common Stock, Crandell is the holder of
                           5,395 shares of Common Stock, and Nelsen is the
                           record owner of 10,395 shares of Common Stock and
                           owns an option that is exercisable to purchase 7,500
                           shares of Common Stock ("Option Shares").

                               Page 8 of 15 Pages



------------------                                            ------------------
CUSIP NO. 45232710                      13G                   PAGE 9 OF 15 PAGES
------------------                                            ------------------

                  (b)      Percent of class:

                           Each reporting person except the Managing Directors:
                           10.09%. Each of the Managing Directors, excluding
                           Nelsen: 10.11%. Nelsen: 10.14%. The foregoing
                           percentages are calculated based on the 32,850,123
                           shares of Common Stock reported to be outstanding in
                           the Issuer's Form 10-Q filed with the Securities and
                           Exchange Commission on November 4, 2003 (the
                           "Reported Shares"). Nelsen's percentage is calculated
                           based on 32,857,623 shares, which included the
                           Reported Shares and the Option Shares.

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

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

                                    0 shares for each Reporting Person except
                                    the Managing Directors. 4,625 shares for
                                    Lazarus, 5,088 shares for Bybee, 5,395
                                    shares for Crandell and 17,895 shares for
                                    Nelsen, which includes the Option Shares.

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

                                    Each of the Reporting Persons:  3,315,298.

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

                                    0 shares for each Reporting Person except
                                    the Managing Directors. 4,625 shares for
                                    Lazarus, 5,088 shares for Bybee, 5,395
                                    shares for Crandell and 17,895 shares for
                                    Nelsen, which includes the Option Shares.

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

                                    Each of the Reporting Persons: 3,315,298.

                  Each Reporting Person disclaims beneficial ownership of such
                  shares of Common Stock except for the shares, if any, such
                  Reporting Person holds of record.

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.

                  Not Applicable.

Item 7.           Identification and Classification of the Subsidiary which
                  Acquired the Security Being Reported on By the Parent Holding
                  Company or Control Person.

                  Not Applicable.

Item 8.           Identification and Classification of Members of the Group.

                               Page 9 of 15 Pages



------------------                                           -------------------
CUSIP NO. 45232710                      13G                  PAGE 10 OF 15 PAGES
------------------                                           -------------------

                  Not Applicable. The Reporting Persons expressly disclaim
                  membership in a "group" as used in Rule 13d-1(b)(ii)(J).

Item 9.           Notice of Dissolution of Group.

                  Not Applicable.

Item 10.          Certification.

                  Not Applicable. This statement on Schedule 13G is not filed
                  pursuant to Section 240.13d-1(b) nor Section 240.13d-1(c).

                               Page 10 of 15 Pages



------------------                                           -------------------
CUSIP NO. 45232710                      13G                  PAGE 11 OF 15 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 11, 2004

                                            ARCH VENTURE FUND III, L.P.

                                            By: ARCH Venture Partners, L.L.C.
                                                its General Partner

                                                By:               *
                                                    ----------------------------
                                                    Steven Lazarus
                                                    Managing Director

                                            ARCH VENTURE PARTNERS, L.L.C.

                                                By:               *
                                                    ----------------------------
                                                    Steven Lazarus
                                                    Managing Director

                                                         *
                                            ----------------------------
                                              Steven Lazarus

                                                         *
                                            ----------------------------
                                              Keith Crandell

                                                         *
                                            ----------------------------
                                              Robert Nelsen

                                                         *
                                             ---------------------------
                                              Clinton Bybee

                                                     * By: /s/ Mark McDonnell
                                                           ---------------------
                                                           Mark McDonnell as
                                                           Attorney-in-Fact

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

This Schedule 13G was executed by Mark McDonnell pursuant to Powers of Attorney
attached hereto as Exhibit 2 and incorporated herein by reference.

                               Page 11 of 15 Pages