Lexicon Genetics Broadens Patent Portfolio with New Patent on Gene Targeting

With the issuance of the 610 patent, Lexicon has broad exclusive rights in certain fields under eight U.S. patents covering aspects of gene targeting. “The 610 patent, in combination with the previously-issued patents covering positive-negative selection, addresses the practical applications of Dr. Mario Capecchi’s groundbreaking invention as utilized in the pharmaceutical and biotechnology industries,” said Arthur T. Sands, M.D., Ph.D., president and chief executive officer of Lexicon.

Lexicon uses its proprietary gene knockout technology to systematically discover the physiological functions of genes in mice and to identify which corresponding genes encode potential targets for therapeutic intervention. To date, Lexicon has knocked out and phenotypically characterized more than 1,500 genes as part of its Genome5000™ program, deriving more than 40 drug discovery programs in the fields of diabetes, obesity, cardiovascular disease, psychiatric and neurological disorders, cancer, immune system disorders and ophthalmic disease.

Lexicon’s gene targeting technologies, including the technology covered by the 610 patent, are widely used in the pharmaceutical and biotechnology industries. Lexicon has granted non-exclusive, internal research-use sublicenses under its gene targeting patents to a number of leading pharmaceutical and biotechnology companies, including Pfizer Inc, GlaxoSmithKline plc, Merck & Co., Inc., Aventis Pharmaceuticals, Inc., Amgen, Inc., Genentech, Inc., Biogen Idec Inc., Millennium Pharmaceuticals, Inc., AstraZeneca and others.

About Lexicon Genetics

Lexicon Genetics is a biopharmaceutical company focused on the discovery of breakthrough treatments for human disease. Lexicon is using gene knockout technology to systematically discover in living mammals, or in vivo, the physiological functions and pharmaceutical utility of genes. The Company’s gene function discoveries fuel therapeutic discovery programs in diabetes, obesity, cardiovascular disease, psychiatric and neurological disorders, cancer, immune system disorders and ophthalmic disease. Lexicon has established drug discovery alliances and functional genomics collaborations with leading pharmaceutical and biotechnology companies, research institutes and academic institutions throughout the world to commercialize its technology and turn its discoveries into drugs. Additional information about the Company is available through Lexicon’s corporate website, www.lexicon-genetics.com.

Safe Harbor Statement

This press release contains “forward-looking statements,” including statements about Lexicon’s growth and future operating results, discovery and development of products, strategic alliances, and intellectual property, as well as other matters that are not historical facts or information. These forward-looking statements are based on management’s current assumptions and expectations and involve risks, uncertainties and other important factors, specifically including those relating to Lexicon’s ability to develop drug candidates from its discoveries, achieve its operational objectives, obtain patent protection for its discoveries and establish strategic alliances, that may cause Lexicon’s actual results to be materially different from any future results expressed or implied by such forward-looking statements. Information identifying such important factors is contained under “Factors Affecting Forward-Looking Statements” and “Business – Risk Factors” in Lexicon’s annual report on Form 10-K for the year ended December 31, 2002, as filed with the Securities and Exchange Commission. Lexicon undertakes no obligation to update or revise any such forward-looking statements, whether as a result of new information, future events or otherwise.

Copyright 2002 - 2003 Lexicon Genetics Incorporated

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