ChemoCentryx Presents Positive Results from Phase 1 Clinical Studies of Traficet-EN^™ at Digestive Disease Week Meeting

Traficet-EN^™ Is Well-Tolerated and Appropriate for Once-Daily Oral Dosing

Chicago, IL; May 16, 2005 — ChemoCentryx, Inc. presented positive Phase 1 clinical and preclinical data from studies of the company's lead product for inflammatory bowel disease (IBD), Traficet-EN^™ (CCX282) at the Digestive Disease Week 2005 conference being held in Chicago, Illinois May 14-19, 2005. These data indicate that Traficet-EN^™ is highly efficacious in models of Crohn's disease and ulcerative colitis. Traficet-EN^™ is a highly potent and selective inhibitor of the CCR9 chemokine receptor, which is specifically expressed on inflammatory cells homing to the digestive tract. In addition, Phase 1 study data indicate that Traficet-EN^™ is well tolerated and that the drug's pharmacokinetic properties allow for once-daily dosing in a capsule form.

"We believe Traficet-EN^™ has tremendous potential as a novel, effective and convenient treatment for patients with inflammatory bowel disease," said Thomas J. Schall, Ph.D., President and CEO of ChemoCentryx. "As indicated by the data presented at the Digestive Disease Week meeting, Traficet-EN^™ has some excellent qualities, including high oral bioavailability as well as the ability to target the inflammatory activity underlying IBD. Based on these encouraging data and interest from leading investigators, we have a Phase 2 clinical study underway as well as plans in place to begin the next phase of clinical trials later this year among patients with moderate to severe Crohn's disease."

ChemoCentryx scientists presented these data in a poster entitled "A New Approach for Oral Therapy in IBD: Traficet-EN^™, An Antagonist for CCR9 - Efficacy in Preclinical Models and Early Clinical Data". The poster session took place on Sunday, May 15, 2005.

About Traficet-EN^™
Traficet-EN^™, a first-in-class small molecule drug, is designed to control the inappropriate inflammation in digestive tract tissues which underlies IBD. Unlike many other existing and emerging IBD therapeutics, which are given by injection or infusion, Traficet-EN^™ is designed to be taken by mouth once a day. By selectively binding to CCR9, a chemokine receptor restricted to inflammatory cells found in the large and small intestine and involved in the homing of these cells to the digestive tract, Traficet-EN^™ has been shown to be efficacious in models of Crohn's disease and ulcerative colitis (the two principal forms of IBD). In preclinical studies, the compound worked both therapeutically and prophylactically.

A Phase 2 clinical study to evaluate Traficet-EN^™'s safety and tolerability among patients and to monitor certain indicators of clinical activity is currently underway. ChemoCentryx plans to initiate the next phase of clinical development to evaluate Traficet-EN^™'s efficacy and safety later this year.

About Inflammatory Bowel Disease
Inflammatory bowel disease (IBD) is a chronic condition that features relapsing inflammation of the gastrointestinal tract. IBD consists of two forms - Crohn's disease and ulcerative colitis - and affects at least 1.7 million patients in North America and Europe. Currently, no cure exists for IBD, and, in the most severe cases, cumulative damage to the intestine can result in the need for surgical intervention. Despite the introduction of Tumor Necrosis Factor (TNF) inhibitors, many patients do not respond to current treatment options, find them difficult to use, or will develop serious long-term side effects. As a small molecule taken orally once a day, ChemoCentryx's Traficet-EN^™ is expected to provide advantages in terms of dosing, compliance, and cost over existing biologic therapeutics.

About ChemoCentryx
ChemoCentryx, Inc. discovers, develops and commercializes novel small molecule medicines for autoimmune diseases, inflammatory disorders and cancer. Based on the company's leadership position in the chemokine field, ChemoCentryx has built a pipeline of highly selective, orally-available drugs designed to inhibit the specific chemokine activity associated with a given condition, resulting in potentially safer, more efficacious treatments. The company's most advanced product, Traficet-EN^™, for inflammatory bowel disease, is currently undergoing Phase 2 clinical evaluation. The company is also advancing several development candidates for cancer and cardiopulmonary inflammation. ChemoCentryx has established partnerships with Forest Laboratories and Amgen to develop new medicines for autoimmune and inflammatory diseases. ChemoCentryx is privately held with headquarters in Mountain View, California. For more information on the company, visit www.chemocentryx.com.

Any statements in this press release about ChemoCentryx's expectations, beliefs, plans, objectives, assumptions or future events or performance are not historical facts and are forward-looking statements. These statements are often, but not always, made through the use of words or phrases such as "believe," "will," "expect," "anticipate," "estimate," "intend," "plan," and "would." Forward-looking statements are not guarantees of performance. They involve known and unknown risks, uncertainties and assumptions that may cause actual results, levels of activity, performance or achievements to differ materially from any results, levels of activity, performance or achievements expressed or implied by any forward-looking statement. Some of the risks, uncertainties and assumptions that could cause actual results to differ materially from estimates or projections contained in the forward-looking statements include but are not limited to (i) the timing, success and cost of preclinical research and clinical studies, (ii) the timing, acceptability and review periods for regulatory filings, (iii) the availability of corporate partners, (iv) uncertainties relating to patent protection and intellectual property rights of third parties, (v) the impact of competitive products and technological changes, (vi) the availability of capital and the cost of capital, (vii) other vagaries in the biotechnology industry and (viii) other risks. ChemoCentryx undertakes no obligation to update or revise any forward-looking statements.