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Rigel Delivers Additional Respiratory Drug Research Targets and Completes Discovery Phase of Target Identification Collaboration with Pfizer

-- Rigel receives milestone payments for six additional targets --

South San Francisco, Calif., - May 06, 2002

LRigel Pharmaceuticals, Inc. (NASDAQ: RIGL) today announced that it has delivered six additional validated drug targets to Pfizer Inc. (NYSE: PFE), thereby completing its discovery phase respiratory disease research collaboration. Rigel will receive milestone payments for these targets that may now enter the next phases of preclinical research and development at Pfizer. Other financial terms were not disclosed.

“Rigel’s team has delivered on its milestones in this collaboration to discover new targets for respiratory disorders, such as asthma and allergy,” said James M. Gower, chairman and chief executive officer of Rigel. “We are hopeful that the targets that we have provided to Pfizer will result in the development of novel drugs that address this multi-billion dollar disease market.”

The two companies originally entered into an agreement in January 1999 to use Rigel’s peptide libraries to identify intracellular drug targets that control the production of IgE, a key mediator in allergic reactions and asthma in B cells. Under the terms of the agreement, Pfizer provided research funding to Rigel as well as certain research milestone payments. Rigel will also receive royalty payments relating to the development and commercialization of any human or animal therapeutics resulting from the collaboration. In return, Pfizer will have worldwide rights to develop and market human and veterinary drugs against the targets that inhibit IgE class switching in B cells.

About Rigel Pharmaceuticals, Inc.
Rigel Pharmaceuticals, Inc. (www.rigel.com) is a drug discovery and development company that uses advanced functional genomics tools to discover novel drug targets that can be used to develop orally administered small molecule drugs. Rigel’s technology is designed to identify molecules that play an important role in regulating a human cell's response to disease by testing a very large number of proteins in a very large number of cells to determine which proteins will change a cell’s response to the disease. Rigel currently has ten product development programs underway, with five programs being proprietary programs in the areas of asthma/allergy, rheumatoid arthritis and inflammatory bowel disease, cancerous tumor growth and hepatitis C. Rigel expects to begin clinical trials during 2002 with one or more drug candidates from these five programs. In addition to the Rigel-owned programs, the company has five joint programs with its corporate partners in the product development areas of asthma/allergy, autoimmunity, transplant rejection and two programs in cancerous tumor growth. With Rigel’s support, one of the company’s partners is conducting an additional program in chronic bronchitis at its premises. Rigel has multi-year collaborations with Pfizer Inc., Cell Genesys, Inc., Johnson & Johnson Pharmaceutical Research & Development, L.L.C. and Novartis Pharma A.G. Rigel is based in South San Francisco, California.

This press release contains "forward-looking" statements, including statements related the anticipated development and success of drugs resulting from targets delivered to Pfizer and Rigel’s plans to commence clinical trials in 2002. Any statements contained in this press release that are not statements of historical fact may be deemed to be forward-looking statements. Words such as "believes," "anticipates," "plans," "expects," "will" and similar expressions are intended to identify forward-looking statements. There are a number of important factors that could cause Rigel’s results to differ materially from those indicated by these forward-looking statements, including the risks detailed from time to time in Rigel’s SEC reports, including its Annual Report on Form 10-K for the year ended December 31, 2001. Rigel does not undertake any obligation to update forward-looking statements