Rigel Announces Completion of R788 plus Methotrexate Drug Interaction Study in Patients with Rheumatoid Arthritis

Company to Initiate Further Clinical Studies of R788 in Rheumatoid Arthritis and in Immune Thrombocytopenic Purpura Later This Year

SOUTH SAN FRANCISCO, Calif. - February 22, 2006

Rigel Pharmaceuticals, Inc. (Nasdaq: RIGL) today announced preliminary data from a Phase I double-blind, placebo controlled trial to investigate the safety and pharmacokinetics of R788, an oral syk kinase inhibitor, in combination with methotrexate in rheumatoid arthritis (RA) patients. The data demonstrated that R788 was well tolerated when given in combination with methotrexate and had no significant adverse pharmacokinetic interactions. The company also announced plans to initiate separate clinical efficacy studies with R788, in RA and in Immune Thrombocytopenic Purpura (ITP), in the second half of 2006.

“New, effective therapeutic options in RA are greatly needed since current treatments have potentially significant limitations,” stated Elliott B. Grossbard, M.D., senior vice president of medical development at Rigel. “We are pursuing R788 in autoimmune diseases such as RA and ITP because it has been shown to be a potent and selective inhibitor of syk kinase, which may play a key role in autoimmune diseases.”

The Phase I study enrolled patients verified to suffer from RA and who were receiving methotrexate treatment. There were no unanticipated adverse events and pharmacokinetic analysis suggests that there is no adverse interaction with the two agents.

About R788
R788 is a novel, oral syk kinase inhibitor that blocks the activation of mast cells, macrophages and B cells that promote swelling and an inflammatory response. It is being developed initially to treat RA. Phase I trial results have demonstrated that R788 is well-tolerated and showed good pharmaceutical properties. Earlier Phase I studies generated valuable pharmacokinetic/pharmacodynamic data establishing a strong correlation between drug plasma levels and the inhibition of the drug target. In preclinical studies, Rigel’s compound greatly diminished the swelling and tissue destruction associated with RA. In addition, in a murine model of ITP, the drug increased platelet counts significantly.

Rheumatoid Arthritis: Current Treatments and Market Opportunity
Approximately 2.1 million people in the U.S. suffer from RA and the worldwide market for innovative RA drugs is projected to reach $10 billion by 2008. RA is a chronic inflammatory disease that affects multiple tissues, but typically produces its most pronounced symptoms in the joints. It is often progressive and debilitating, preventing people from living a symptom-free life. Ultimately the chronic inflammation of joints leads to the destruction of the soft tissue and erosion of the articular surfaces of the bone.

The current treatment options for RA have potentially significant side effects and other shortfalls, including gastrointestinal complications and kidney damage. Some RA patients currently receive multiple drugs depending on the extent and aggressiveness of the disease. Most RA patients require some form of DMARD— including methotrexate, an anti-cancer agent, or TNF-blocking agents such as Enbrel®. The TNF-blocking agents only inhibit the inflammatory mediator TNF, and are all delivered via injection. Rigel believes that there is a significant opportunity for an oral DMARD that can be used earlier in the course of the disease, preventing its progression prior to major bone and cartilage destruction; this is the product goal for R788 in RA.

About Rigel (www.rigel.com)
Rigel is a clinical-stage drug development company that discovers and develops novel, small-molecule drugs for the treatment of inflammatory diseases, cancer and viral diseases. Our goal is to move one new product candidate for a significant indication into the clinic each year. We have achieved this goal since 2002. Our pioneering research focuses on intracellular signaling pathways and related targets that are critical to disease mechanisms. Rigel’s productivity has resulted in strategic collaborations with large pharmaceutical partners to develop and market our product candidates. We have product development programs in inflammatory/autoimmune diseases such as rheumatoid arthritis, thrombocytopenia, asthma and allergy, as well as in cancer.

This press release contains "forward-looking" statements, including statements related to Rigel's plans to pursue clinical development of product candidates and the timing thereof and the potential efficacy and safety of product candidates, and the opportunity of a DMARD. 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 "plans," "intends," "expects," “believes,” “goal,” “suggests,” and similar expressions are intended to identify these 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 risks associated with the timing and success of pre-clinical studies and clinical trials, as well as other risks detailed from time to time in Rigel's SEC reports, including its Quarterly Report on Form 10-Q for the quarter ended September 30, 2005. Rigel does not undertake any obligation to update forward-looking statements.

Contact: Raul Rodriguez
Phone: 650.624.1302
Email: invrel@rigel.com

Media Contact: Carolyn Bumgardner Wang, WeissComm Partners, Inc.
Phone: 415.946.1065
Email: carolyn@weisscommpartners.com