The Woodlands, Texas, October 5, 2005 – Lexicon Genetics Incorporated (Nasdaq: LEXG) announced today that it has entered into a three-year contract to provide selected knockout mouse lines and related phenotypic data to the United States National Institutes of Health (NIH).  NIH will make these materials available to researchers at academic and other non-profit research institutions to accelerate the determination of gene function and the understanding of human disease.  NIH is obtaining these materials from Lexicon as a first step in its recently announced Knockout Mouse Project, which has a goal of obtaining a knockout for every gene.  

Under the contract, NIH may select lines of knockout mice and related phenotypic data from among lines that Lexicon has elected to make available.  These materials are related to genes that have already been knocked out and analyzed by Lexicon.  Lexicon will receive payment from NIH of approximately $4.9 million for NIH’s initial order of knockout mouse lines.  Lexicon retains the sole right to provide these materials to commercial entities. 

Lexicon owns or controls rights under 16 issued U.S. patents relating to technologies for the generation of knockout mice.  The NIH contract and the creation of the Texas Institute for Genomic Medicine are part of Lexicon’s strategy to provide access to specific components of its genetic technology portfolio as it advances its drug discovery programs into clinical development. 

“Since its founding in 1995, Lexicon’s core premise has always been that knocking out the mouse genome is the key to understanding the functions of human genes,” said Brian P. Zambrowicz, Ph.D., executive vice president of research at Lexicon.  “NIH’s recently announced Knockout Mouse Project demonstrates increasing consensus on the importance of this approach for scientific and medical research.  The scale of our knockout mouse generation and analysis capabilities and our strong intellectual property estate allow Lexicon to provide a means by which NIH can accelerate its basic research initiatives.”

About Lexicon Genetics

Lexicon Genetics is a biopharmaceutical company focused on the discovery and development of breakthrough treatments for human disease.  Lexicon is systematically discovering the physiological and behavioral functions of genes to identify potential points of therapeutic intervention, or drug targets.  Lexicon makes these discoveries using its proprietary gene knockout technology to model the physiological effects that could be expected from prospective drugs directed against novel targets.  The Company has advanced knockout-validated targets into drug discovery programs in six therapeutic areas:  diabetes and obesity, cardiovascular disease, psychiatric and neurological disorders, cancer, immune system disorders and ophthalmic disease.  Lexicon is working both independently and through strategic collaborations and alliances to accelerate the development and commercialization of its discoveries.  Additional information about Lexicon is available through its corporate website, www.lexicon-genetics.com.

About NIH

The National Institutes of Health (NIH) -- "The Nation’s Medical Research Agency" -- includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services.  It is the primary Federal agency for conducting and supporting basic, clinical and translational medical research, and it investigates the causes, treatments and cures for both common and rare diseases.  More information about NIH and its programs is available at www.nih.gov.

Lexicon Genetics 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 successfully conduct preclinical development of its drug candidates and advance such candidates into clinical development, achieve its operational objectives, obtain patent protection for its discoveries and establish strategic alliances, as well as those relating to manufacturing, the regulatory process, intellectual property rights, and the therapeutic or commercial value of its drug candidates, 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, 2004, 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.