European institutions aimed at cancer research and control are spending sizable resources to develop preclinical and clinical chemoprevention trials. Pilot studies showed positive effect on colorectal cell proliferation from supplementation with calcium; vitamins A, C, and E; omega-3 fatty acids; and folic acid. A significant reduction in adenoma recurrence after polypectomy was found in patients randomly assigned to take vitamin A, C, and E supplementation or, to a lesser extent, lactulose. Although first reports showed a disquieting higher incidence of lung cancer in male smokers who took beta-carotene supplementation, the European Organization of Research and Treatment of Cancer (EORTC) planned a chemoprevention study on the prevention of second primary tumors in patients with curatively treated head and neck or lung cancer (EUROSCAN). Retinol palmitate or N-acetylcysteine or both are given for two years. The European Cancer Prevention Organization (ECP) is carrying out a clinical trial in patients with previous adenomas of the large bowel, to test the efficacy of calcium or fiber supplementation on adenoma recurrence. ECP in collaboration with EURONUT has also started a multinational intervention study of the effect of H. pylori eradication and/or dietary supplementation with vitamin C on intestinal metaplasia.