Gastric cancer is the second leading cause of cancer deaths in the World. In China, gastric cancer exceeds all other cancer mortality except lung cancer. Helicobacter pylori infection is an important cause of gastric cancer. We have previously started a randomized placebo-controlled chemoprevention trial in Changle in 1994 to address the issue of whether eradication of H. pylori alone is able to prevent or reduce the risk of gastric cancer. The project involved 1600 subjects and is still ongoing. On the other hand, our laboratory research indicated that an abnormally high expression of an enzyme cyclooxygenase-2 was found in gastric cancer and inhibition of this enzyme by a new drug (specific cyclooxygenase-2 inhibitor) could kill the cancer cells. The same drug is approved now for use in treatment of hereditary colon cancer syndrome (Familial Adenomatous Polyposis, FAP), in the same rationale of tumour suppressive property of this drug. We are now initiating a second chemoprevention study to assess the addition of this specific cyclooxygenase-2 inhibitor together with eradication of H. pylori on prevention or reduction of the risk of gastric cancer and to assess whether the combination can reverse pre-cancerous lesions in the stomach in the high-risk population. The proposed site is Shangdong, China with very high prevalence of pre-cancerous lesions in asymptomatic H. pylori carriers. We plan to recruit 1500 H. pylori positive subjects for this randomized placebo-controlled study. H. pylori carriers will be randomized to receive treatment for the infection or placebo, followed by specific COX-2 inhibitor or placebo for 3 years. The results will have significant impact on prevention of gastric cancer on a national scale and worldwide.