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Rigel Achieves Milestone with Merck Ligase Collaboration

SOUTH SAN FRANCISCO, Calif. - January 30, 2006

Rigel Pharmaceuticals, Inc. (Nasdaq: RIGL) announced today that it has received a milestone payment from Merck & Co., Inc. (NYSE: MRK) as part of their collaboration to investigate ubiquitin ligases, a new class of drug targets, to find treatments for cancer and potentially other diseases.

Rigel is a leader in investigating and characterizing the ubiquitin ligase system for the discovery and development of potential new therapeutics. The collaboration with Merck combines Rigel's capabilities in ubiquitin ligases with Merck's molecular profiling technology and downstream clinical infrastructure to explore this promising new class of drug targets.

“We believe this is one of the largest dedicated efforts focused on ligases by a pharmaceutical or biotech enterprise and it is proving to be a highly productive collaboration exploring ligases and potential therapeutics in cancer,” said Donald G. Payan, M.D., executive vice president and chief scientific officer of Rigel.

Under the terms of the agreement, Rigel received an initial cash payment and funding for Rigel research scientists for two and a half years and is also eligible to receive milestone payments for preclinical and clinical events. Merck is responsible for worldwide development and commercialization of any resulting compounds and will pay Rigel royalties on future product sales, if any. The collaboration is based on a number of new targets designated by Merck and do not include Rigel's current ligase targets. Additional terms were not disclosed.

About Ubiquitin Ligases
Ubiquitin ligases are enzymes that regulate protein degradation within the cell. Breakdown of proteins, in turn, affects many important cellular functions, including cell division. Targeting ligases represents a novel approach to treating diseases where normal cellular processes are out of balance. Because unchecked cell division is the hallmark of cancer, researchers believe that this part of the cell machinery represents a particularly compelling target for cancer therapies. Ubiquitin ligase targets are numerous and modular. This provides the potential for intervening in a highly specific fashion in a disease, potentially improving efficacy and minimizing side-effects.

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 allergy/asthma, rheumatoid arthritis and cancer.

This press release contains "forward-looking" statements, including statements related to possible milestones and royalties, Rigel's plans to pursue clinical development of product candidates and the timing thereof and the potential efficacy of product candidates. 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" 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