South San Francisco, California
July 31, 2002

- Genoptera Joint Venture Has Delivered More Than 50 Validated Pesticide Targets

Exelixis, Inc. (Nasdaq: EXEL) has delivered novel assays based on validated pesticide targets for Bayer AG (NYSE: BAY). Exelixis and Bayer's crop protection division established a joint venture, Genoptera, two years ago to facilitate the discovery of novel pesticides. High throughput screening of
these targets against Bayer's extensive compound collection may lead to the development of superior pest control agents. The delivery of these assays has triggered an undisclosed milestone payment to Exelixis.

"We have made significant, rapid progress in our collaboration with Bayer and we believe that we have made a significant contribution to Bayer's in-house discovery efforts," said George A. Scangos, president and chief executive officer, Exelixis. "Together, we have identified more than 250 potential target genes that are in the process of being validated. To date, more than 50 validated targets have been delivered to Bayer. Some of these targets belong to well known insecticide target families such as ion channels or receptors. More importantly, most of these new targets belong to novel target families and offer greater opportunity for innovation. Bayer is actively screening these new targets with the goal to produce important hits and leads."

Genoptera LLC is an Exelixis-Bayer joint venture with the aim of identifying novel targets and providing assays for the discovery of new crop protection substances, in particular the discovery of novel insecticides and nematicides. The 2000 joint venture included a $20 million up-front payment and performance-based milestone and royalty payments to Exelixis as well as $80 million in research funding over the course of the eight-year joint venture.

Exelixis, Inc. is a leading genomics-based drug discovery company focused on product 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 they encode. The company's technology is broadly applicable to all life sciences industries including pharmaceutical, diagnostic, agricultural biotechnology and animal health. Exelixis has partnerships with Bayer CropScience, Bristol-Myers Squibb, Cytokinetics, Dow
Agrosciences, Elan Pharmaceuticals, Merck, Protein Design Labs, Schering-Plough Research Institute and Scios and is building its internal development program in the area of oncology.

Exelixis and the Exelixis logo are registered U.S. trademarks.