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

                                   FORM 10-K/A
                                (AMENDMENT NO. 1)

(MARK ONE)

[X]   ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE
      ACT OF 1934

      FOR THE FISCAL YEAR ENDED DECEMBER 31, 2003

                                       OR

[ ]   TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
      EXCHANGE ACT OF 1934

      FOR THE TRANSITION PERIOD FROM _____________ TO _____________

                        COMMISSION FILE NUMBER: 000-30111

                          LEXICON GENETICS INCORPORATED
             (Exact Name of Registrant as Specified in its Charter)

                DELAWARE                                  76-0474169
     (State or Other Jurisdiction of                  (I.R.S. Employer
       Incorporation or Organization)               Identification Number)

8800 TECHNOLOGY FOREST PLACE
THE WOODLANDS, TEXAS 77381                                 (281) 863-3000
(Address of Principal Executive                  (Registrant's Telephone Number,
   Offices and Zip Code)                              Including Area Code)

        SECURITIES REGISTERED PURSUANT TO SECTION 12(b) OF THE ACT: NONE

           SECURITIES REGISTERED PURSUANT TO SECTION 12(g) OF THE ACT:
                    Common Stock, par value $0.001 per share

      Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports) and (2) has been subject to such
filing requirements for the past 90 days. Yes [X] No [ ]

      Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [X]

      Indicate by check mark whether the registrant is an accelerated filer (as
defined in Rule 12b-2 of the Securities Exchange Act of 1934). Yes [X] No [ ]

      The aggregate market value of voting stock held by non-affiliates of the
registrant as of the last day of the registrant's most recently completed second
quarter was approximately $198.3 million, based on the closing price of the
common stock on the Nasdaq National Market on June 30, 2003 of $6.60 per share.
For purposes of the preceding sentence only, all directors, executive officers
and beneficial owners of ten percent or more of the registrant's common stock
are assumed to be affiliates. As of June 30, 2004, 63,409,081 shares of common
stock were outstanding.

                       DOCUMENTS INCORPORATED BY REFERENCE

      No documents are incorporated by reference into this Form 10-K/A.

================================================================================


EXPLANATORY NOTE

      We are filing this amendment to our Annual Report on Form 10-K for the
year ended December 31, 2003, originally filed with the Securities and Exchange
Commission on March 12, 2004, solely for the purpose of filing revised versions
of Exhibits 10.14 and 10.15 to disclose certain information for which
confidential treatment had been initially requested. Pursuant to Rule 12b-15
under the Securities Exchange Act of 1934, as amended, we are including Item 15
below. Except as specifically indicated herein, no other information included in
our Annual Report on Form 10-K for the year ended December 31, 2003 is amended
by this Form 10-K/A.

ITEM 15. EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS ON FORM 8-K

      (a)   Documents filed as a part of this report:

            1.    Consolidated Financial Statements



                                                           PAGE
                                                           ----
                                                        
Report of Independent Auditors.............................F-1
Report of Independent Public Accountants...................F-2
Consolidated Balance Sheets................................F-3
Consolidated Statements of Operations......................F-4
Consolidated Statements of Stockholders' Equity............F-5
Consolidated Statements of Cash Flows......................F-6
Notes to Consolidated Financial Statements.................F-7


      All other financial statement schedules are omitted because they are not
applicable or not required, or because the required information is included in
the financial statements or notes thereto.

      2.    Exhibits



EXHIBIT NO.                              DESCRIPTION
-----------                              -----------
            
    3.1   --   Restated Certificate of Incorporation (filed as Exhibit 3.1 to
               the Company's Registration Statement on Form S-1 (Registration
               No. 333-96469) and incorporated by reference herein).

    3.2   --   Restated Bylaws (filed as Exhibit 3.2 to the Company's
               Registration Statement on Form S-1 (Registration No. 333-96469)
               and incorporated by reference herein).

   10.1   --   Employment Agreement with Arthur T. Sands, M.D., Ph.D. (filed as
               Exhibit 10.1 to the Company's Registration Statement on Form S-1
               (Registration No. 333-96469) and incorporated by reference
               herein).

   10.2   --   Employment Agreement with James R. Piggott, Ph.D. (filed as
               Exhibit 10.2 to the Company's Registration Statement on Form S-1
               (Registration No. 333-96469) and incorporated by reference
               herein).

   10.3   --   Employment Agreement with Jeffrey L. Wade, J.D. (filed as Exhibit
               10.3 to the Company's Registration Statement on Form S-1
               (Registration No. 333-96469) and incorporated by reference
               herein).

   10.4   --   Employment Agreement with Brian P. Zambrowicz, Ph.D. (filed as
               Exhibit 10.4 to the Company's Registration Statement on Form S-1
               (Registration No. 333-96469) and incorporated by reference
               herein).

   10.5   --   Employment Agreement with Julia P. Gregory (filed as Exhibit 10.5
               to the Company's Registration Statement on Form S-1 (Registration
               No. 333-96469) and incorporated by reference herein).

   10.6   --   Employment Agreement with Alan Main, Ph.D. (filed as Exhibit 10.1
               to the Company's Quarterly Report on Form 10-Q for the period
               ended September 30, 2001 and incorporated by reference herein).




EXHIBIT NO.                              DESCRIPTION
-----------                              -----------
            
   10.7   --   Form of Indemnification Agreement with Officers and Directors
               (filed as Exhibit 10.7 to the Company's Registration Statement on
               Form S-1 (Registration No. 333-96469) and incorporated by
               reference herein).

   10.8   --   2000 Equity Incentive Plan (filed as Exhibit 10.8 to the
               Company's Registration Statement on Form S-1 (Registration No.
               333-96469) and incorporated by reference herein).

   10.9   --   2000 Non-Employee Directors' Stock Option Plan (filed as Exhibit
               10.9 to the Company's Registration Statement on Form S-1
               (Registration No. 333-96469) and incorporated by reference
               herein).

  10.10   --   Coelacanth Corporation 1999 Stock Option Plan (filed as Exhibit
               99.1 to the Company's Registration Statement on Form S-8
               (Registration No. 333-66380) and incorporated by reference
               herein).

 +10.11   --   LexVision Database and Collaboration Agreement, dated September
               26, 2000, with Bristol-Myers Squibb Company (filed as Exhibit
               10.1 to the Company's Current Report on Form 8-K dated September
               26, 2000 and incorporated by reference herein).

 +10.12   --   LexVision Database and Collaboration Agreement, dated June 27,
               2001, with Incyte Genomics, Inc. (filed as Exhibit 10.2 to the
               Company's Quarterly Report on Form 10-Q for the period ended June
               30, 2001 and incorporated by reference herein).

 +10.13   --   Therapeutic Protein Alliance Agreement, dated June 27, 2001, with
               Incyte Genomics, Inc. (filed as Exhibit 10.3 to the Company's
               Quarterly Report on Form 10-Q for the period ended June 30, 2001
               and incorporated by reference herein).

*+10.14   --   Amended and Restated Collaboration and License Agreement, dated
               November 19, 2003, with Genentech, Inc.

*+10.15   --   Collaboration and License Agreement, dated December 17, 2003,
               with Bristol-Myers Squibb Company

  10.16   --   Synthetic Lease Financing Facility with First Security Bank,
               National Association, the Lenders and Holders named therein, and
               Bank of America, N.A. (filed as Exhibit 10.12 to the Company's
               Annual Report on Form 10-K for the year ended December 31, 2000
               and incorporated by reference herein).

  10.17   --   Lease Agreement, dated October 21, 1998, between Coelacanth
               Chemical Corporation and ARE-279 Princeton Road, LLC. (filed as
               Exhibit 10.18 to the Company's Annual Report on Form 10-K for the
               year ended December 31, 2001 and incorporated by reference
               herein).

  10.18   --   Lease Agreement, dated May 23, 2002, between Lexicon
               Pharmaceuticals (New Jersey), Inc. and Townsend Property Trust
               Limited Partnership (filed as Exhibit 10.2 to the Company's
               Quarterly Report on Form 10-Q for the period ended June 30, 2002
               and incorporated by reference herein).

   21.1   --   Subsidiaries (filed as Exhibit 21.1 to the Company's Annual
               Report on Form 10-K for the year ended December 31, 2001 and
               incorporated by reference herein).

 **23.1   --   Consent of Ernst & Young LLP

 **23.2   --   Information regarding consent of Arthur Andersen LLP

 **24.1   --   Power of Attorney (contained in signature page)

  *31.1   --   Certification of CEO Pursuant to Section 302 of the
               Sarbanes-Oxley Act of 2002

  *31.2   --   Certification of CFO Pursuant to Section 302 of the
               Sarbanes-Oxley Act of 2002

  *32.1   --   Certification of CEO and CFO Pursuant to Section 906 of the
               Sarbanes-Oxley Act of 2002




EXHIBIT NO.                              DESCRIPTION
-----------                              -----------
            
   99.1   --   Letter to the Securities and Exchange Commission regarding Audit
               Assurances (filed as Exhibit 99.1 to the Company's Annual Report
               on Form 10-K for the year ended December 31, 2001 and
               incorporated by reference herein).


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

*        Filed herewith.

**       Previously filed.

+        Confidential treatment has been requested for a portion of this
         exhibit. The confidential portions of this exhibit have been omitted
         and filed separately with the Securities and Exchange Commission.

         (b)      Reports on Form 8-K:

                  On October 30, 2003, we filed a Current Report on Form 8-K
                  dated October 30, 2003 relating to our issuance of a press
                  release reporting our financial results for the quarter ended
                  September 30, 2003, which press release included our
                  consolidated balance sheet data and consolidated statements of
                  operations data for the period.



                                   SIGNATURES

      Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.

                               LEXICON GENETICS INCORPORATED

Date:  July 16, 2004          By:                *
                                 -----------------------------------------------
                                 Arthur T. Sands, M.D., Ph.D.
                                 President and Chief Executive Officer

Date:  July 16, 2004          By:                *
                                 -----------------------------------------------
                                 Julia P. Gregory
                                 Executive Vice President, Corporate Development
                                 and Chief Financial Officer

      Pursuant to the requirements of the Securities Exchange Act of 1934, this
report has been signed below by the following persons on behalf of the
registrant and in the capacities and on the dates indicated.



              SIGNATURE                                    TITLE                                                 DATE
              ---------                                    -----                                                 ----
                                                                                                       
                  *                      President and Chief Executive Officer                               July 16, 2004
------------------------------------     (Principal Executive Officer)
Arthur T. Sands, M.D., Ph.D.

                  *                      Executive Vice President, Corporate Development and                 July 16, 2004
------------------------------------     Chief Financial Officer
Julia P. Gregory                         (Principal Financial and Accounting Officer)

                  *                      Chairman of the Board of Directors                                  July 16, 2004
------------------------------------
C. Thomas Caskey, M.D.

                  *                      Director                                                            July 16, 2004
------------------------------------
Sam L. Barker, Ph.D.

                  *                      Director                                                            July 16, 2004
------------------------------------
Patricia M. Cloherty

                  *                      Director                                                            July 16, 2004
------------------------------------
Robert J. Lefkowitz, M.D.

                  *                      Director                                                            July 16, 2004
------------------------------------
Alan S. Nies. M.D.


* By:             /s/ Jeffrey L. Wade
         -----------------------------------
                  Jeffrey L. Wade

Pursuant to powers-of-attorney filed on
March 12, 2004 with the Annual Report on
Form 10-K for the year ended December
31, 2003


                                 EXHIBIT INDEX



EXHIBIT NO.                              DESCRIPTION
-----------                              -----------
            
    3.1   --   Restated Certificate of Incorporation (filed as Exhibit 3.1 to
               the Company's Registration Statement on Form S-1 (Registration
               No. 333-96469) and incorporated by reference herein).

    3.2   --   Restated Bylaws (filed as Exhibit 3.2 to the Company's
               Registration Statement on Form S-1 (Registration No. 333-96469)
               and incorporated by reference herein).

   10.1   --   Employment Agreement with Arthur T. Sands, M.D., Ph.D. (filed as
               Exhibit 10.1 to the Company's Registration Statement on Form S-1
               (Registration No. 333-96469) and incorporated by reference
               herein).

   10.2   --   Employment Agreement with James R. Piggott, Ph.D. (filed as
               Exhibit 10.2 to the Company's Registration Statement on Form S-1
               (Registration No. 333-96469) and incorporated by reference
               herein).

   10.3   --   Employment Agreement with Jeffrey L. Wade, J.D. (filed as Exhibit
               10.3 to the Company's Registration Statement on Form S-1
               (Registration No. 333-96469) and incorporated by reference
               herein).

   10.4   --   Employment Agreement with Brian P. Zambrowicz, Ph.D. (filed as
               Exhibit 10.4 to the Company's Registration Statement on Form S-1
               (Registration No. 333-96469) and incorporated by reference
               herein).

   10.5   --   Employment Agreement with Julia P. Gregory (filed as Exhibit 10.5
               to the Company's Registration Statement on Form S-1 (Registration
               No. 333-96469) and incorporated by reference herein).

   10.6   --   Employment Agreement with Alan Main, Ph.D. (filed as Exhibit 10.1
               to the Company's Quarterly Report on Form 10-Q for the period
               ended September 30, 2001 and incorporated by reference herein).




EXHIBIT NO.                              DESCRIPTION
-----------                              -----------
            
   10.7   --   Form of Indemnification Agreement with Officers and Directors
               (filed as Exhibit 10.7 to the Company's Registration Statement on
               Form S-1 (Registration No. 333-96469) and incorporated by
               reference herein).

   10.8   --   2000 Equity Incentive Plan (filed as Exhibit 10.8 to the
               Company's Registration Statement on Form S-1 (Registration No.
               333-96469) and incorporated by reference herein).

   10.9   --   2000 Non-Employee Directors' Stock Option Plan (filed as Exhibit
               10.9 to the Company's Registration Statement on Form S-1
               (Registration No. 333-96469) and incorporated by reference
               herein).

  10.10   --   Coelacanth Corporation 1999 Stock Option Plan (filed as Exhibit
               99.1 to the Company's Registration Statement on Form S-8
               (Registration No. 333-66380) and incorporated by reference
               herein).

 +10.11   --   LexVision Database and Collaboration Agreement, dated September
               26, 2000, with Bristol-Myers Squibb Company (filed as Exhibit
               10.1 to the Company's Current Report on Form 8-K dated September
               26, 2000 and incorporated by reference herein).

 +10.12   --   LexVision Database and Collaboration Agreement, dated June 27,
               2001, with Incyte Genomics, Inc. (filed as Exhibit 10.2 to the
               Company's Quarterly Report on Form 10-Q for the period ended June
               30, 2001 and incorporated by reference herein).

 +10.13   --   Therapeutic Protein Alliance Agreement, dated June 27, 2001, with
               Incyte Genomics, Inc. (filed as Exhibit 10.3 to the Company's
               Quarterly Report on Form 10-Q for the period ended June 30, 2001
               and incorporated by reference herein).

*+10.14   --   Amended and Restated Collaboration and License Agreement, dated
               November 19, 2003, with Genentech, Inc.

*+10.15   --   Collaboration and License Agreement, dated December 17, 2003,
               with Bristol-Myers Squibb Company

  10.16   --   Synthetic Lease Financing Facility with First Security Bank,
               National Association, the Lenders and Holders named therein, and
               Bank of America, N.A. (filed as Exhibit 10.12 to the Company's
               Annual Report on Form 10-K for the year ended December 31, 2000
               and incorporated by reference herein).

  10.17   --   Lease Agreement, dated October 21, 1998, between Coelacanth
               Chemical Corporation and ARE-279 Princeton Road, LLC. (filed as
               Exhibit 10.18 to the Company's Annual Report on Form 10-K for the
               year ended December 31, 2001 and incorporated by reference
               herein).

  10.18   --   Lease Agreement, dated May 23, 2002, between Lexicon
               Pharmaceuticals (New Jersey), Inc. and Townsend Property Trust
               Limited Partnership (filed as Exhibit 10.2 to the Company's
               Quarterly Report on Form 10-Q for the period ended June 30, 2002
               and incorporated by reference herein).

   21.1   --   Subsidiaries (filed as Exhibit 21.1 to the Company's Annual
               Report on Form 10-K for the year ended December 31, 2001 and
               incorporated by reference herein).

 **23.1   --   Consent of Ernst & Young LLP

 **23.2   --   Information regarding consent of Arthur Andersen LLP

 **24.1   --   Power of Attorney (contained in signature page)

  *31.1   --   Certification of CEO Pursuant to Section 302 of the
               Sarbanes-Oxley Act of 2002

  *31.2   --   Certification of CFO Pursuant to Section 302 of the
               Sarbanes-Oxley Act of 2002

  *32.1   --   Certification of CEO and CFO Pursuant to Section 906 of the
               Sarbanes-Oxley Act of 2002





EXHIBIT NO.                              DESCRIPTION
-----------                              -----------
            
   99.1   --   Letter to the Securities and Exchange Commission regarding Audit
               Assurances (filed as Exhibit 99.1 to the Company's Annual Report
               on Form 10-K for the year ended December 31, 2001 and
               incorporated by reference herein).


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

*     Filed herewith.

**    Previously filed.

+     Confidential treatment has been requested for a portion of this exhibit.
      The confidential portions of this exhibit have been omitted and filed
      separately with the Securities and Exchange Commission.