We conducted a randomized, controlled clinical trial to test the efficacy of beta carotene and vitamins C and E in preventing colorectal adenoma, a precursor of invasive cancer.The lack of efficacy of these vitamins argues against the use of supplemental beta carotene and vitamins C and E to prevent colorectal cancer.The primary end points for analyses were new adenomas identified after the first of these two follow-up examinations.751 completed the four-year clinical trial.