Lexicon Genetics Awarded Grant from the United States Army for Study of SMA

The Woodlands, Texas — May 11, 2006 – Lexicon Genetics Incorporated (Nasdaq: LEXG) announced today that it was awarded a grant from the United States Army Medical Research & Materiel Command (USAMRMC) for the identification of targets that may be important in the development of drugs to prevent or treat spinal muscular atrophy (SMA), a neurodegenerative disorder and the leading genetic cause of death in early childhood. Lexicon will receive $2.0 million in funding for the one-year initial term of the grant.

SMA is characterized by a mutation in the SMN1 gene that leads to neurodegeneration. Under the grant, Lexicon will utilize its proprietary gene knockout technology to identify genes that, when knocked out, lead to increased levels of mouse Smn protein. Genes that regulate Smn protein in mice may be involved in the regulation of SMN2 protein in humans. Identification of these genes may enable the development of drugs designed to increase levels of human SMN2 protein to offset the absence of human SMN1 protein and prevent or treat SMA. Lexicon will study approximately 750 pharmaceutically tractable genes in the research program. Lexicon has also entered into an agreement with the SMA Foundation for the potential development of drugs based on discoveries resulting from the program.

“Under this grant, we will utilize Lexicon’s proprietary gene knockout technology to study genes that may impact the function of motor neurons to advance treatments for spinal muscular atrophy,” said Brian P. Zambrowicz, Ph.D., executive vice president of research at Lexicon. “Through this research, we believe we will be able to provide the Army with information relevant to its efforts to treat neurodegenerative diseases and nerve damage.”

Spinal muscular atrophy is a genetic, motor-neuron disease characterized by the wasting of skeletal muscles. Caused by progressive degeneration of nerve cells in the spinal cord, the disease leads to increasing muscular weakness and atrophy and premature death due to respiratory problems. The SMA Foundation estimates that there are currently over 50,000 people suffering from SMA in the United States, Europe and Japan.

SMA research and therapeutics development may be applicable to other neurodegenerative diseases, such as amyotrophic lateral sclerosis (also known as Lou Gehrig’s disease) and Alzheimer’s disease, and may have military relevance. Treatments that protect and maintain neurons or encourage nerve recovery may be important in spinal cord injury and traumatic brain injury. These treatments also have potential for treating nerve damage resulting from chemical weapons such as sarin, nerve gas and other chemical agents.

About Lexicon Genetics

Lexicon Genetics is a biopharmaceutical company focused on discovering and developing 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 addressing these targets. For targets that the company believes have high pharmaceutical value, it engages in programs for the discovery and development of small molecule, antibody and protein drugs. Lexicon 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 collaborations and strategic 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 the Spinal Muscular Atrophy Foundation

Founded in 2003, the Spinal Muscular Atrophy Foundation is a nonprofit organization dedicated to accelerating progress towards a treatment and cure for spinal muscular atrophy through targeted funding of clinical research and novel drug development efforts. Since its inception, the Foundation has awarded over $30 million in sponsored research agreements. In addition, the Foundation is committed to raising awareness and generating support for increased research efforts in SMA among the leaders of industry and government. For more information on the Spinal Muscular Atrophy Foundation, visit www.smafoundation.org or call (646) 253-7100.

About USAMRMC

The United States Army Medical Research & Materiel Command (USAMRMC), located at Fort Detrick, Maryland, conducts research to deliver the medical solutions to enhance, protect and treat the warfighter. USAMRMC strives to shape future medical solutions through research, advanced technology and partnerships. Its goal is to ensure that U.S. military forces are deployed in a state of optimal health and are equipped to protect themselves from disease and injury.

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, 2005, 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.

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