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                                                                    EXHIBIT 99.2

                                  CERTIFICATION

      Pursuant to Section 906 of the Sarbanes-Oxley Act of 2002 (18 U.S.C. 1350,
as adopted), Arthur T. Sands, M.D., Ph.D., Chief Executive Officer of Lexicon
Genetics Incorporated ("Lexicon"), and Julia P. Gregory, Chief Financial Officer
of Lexicon, each hereby certify that:

      1.    Lexicon's Annual Report on Form 10-K for the year ended December 31,
            2002, and to which this Certification is attached as Exhibit 99.2
            (the "Periodic Report"), fully complies with the requirements of
            section 13(a) or section 15(d) of the Securities Exchange Act of
            1934, and

      2.    The information contained in the Periodic Report fairly presents, in
            all material respects, the financial condition and results of
            operations of Lexicon.

      IN WITNESS WHEREOF, the undersigned have set their hands hereto as of the
17th day of March, 2003.


                                   By:  /s/ ARTHUR T. SANDS
                                      ------------------------------------------
                                        Arthur T. Sands, M.D., Ph.D.
                                        President and Chief Executive Officer


                                   By:  /s/ JULIA P. GREGORY
                                      ------------------------------------------
                                        Julia P. Gregory
                                        Executive Vice President and
                                        Chief Financial Officer

