South San Francicso
August 10, 2000

Exelixis, Inc. today announced that Genoptera, the joint venture between Exelixis and Bayer AG's crop protection business group, has selected several novel insecticide targets for assay development and screening. This selection marks an important research accomplishment within the joint venture and triggers an undisclosed milestone payment to Exelixis.

``We are delighted with the rapid progress of Genoptera, which in just seven months has identified many novel pesticide targets,'' said Dr. Detlef Wollweber, head of crop protection research at Bayer AG. ``The Exelixis technology platform takes a unique approach to target discovery, one which we believe will provide us with a distinct advantage as we move these targets into screening and development.''

``Through Genoptera, we believe that our proprietary technology will continue to provide unique insecticide targets that would be difficult to generate using alternative technology,'' stated George A. Scangos, Ph.D., president and chief executive officer of Exelixis. ``With the selection of these targets, we have now made significant progress in three major collaborations -- Bristol-Myers Squibb, Pharmacia and Bayer -- and expect to continue to deliver on these as well as our proprietary program in oncology this year.''

Genoptera LLC was originally formed in January 2000 to discover novel insecticides and nematicides. The joint venture is a continuation and expansion of the collaboration that Exelixis and Bayer initially established in April 1998 and expanded in June 1999. In addition to $80 million in committed research funding over the course of the eight-year joint venture, Exelixis receives performance-based milestone and royalty payments from Bayer. Bayer has the exclusive right to commercialize insecticides based on technology developed by Genoptera.

Bayer is a diversified, international chemicals and health care group, offering a wide variety of products and services from its Health Care, Agriculture, Polymers and Chemicals business segments. In 1999, Bayer employed a worldwide workforce of 120,000 and recorded sales of EUR 27.32 billion.

Exelixis, Inc. is a leading biotechnology company focused on the life sciences industries and development through its expertise in comparative genomics and model system genetics. These technologies provide a rapid, efficient and cost-effective way to move from DNA sequence data to knowledge about the function of genes and the proteins that they encode. The company's technology is broadly applicable to all life science industries including pharmaceutical, diagnostic, agricultural biotechnology and animal health. Exelixis has partnerships with Bayer, Pharmacia, Bristol-Myers Squibb and Dow AgroSciences and is building its internal development program in the area of oncology.