The design of a population screening study, including endoscopic screening for polyps in the rectum and sigmoid colon, was tested in a defined population sample of 200 women and 200 men aged 50-59 years. The attendance rate was 81%. A simple bowel cleansing procedure performed immediately before the examination gave satisfactory conditions for endoscopic examination in 94% of attendants. Polyp prevalence was 35%. The present material and results represent the basis for further follow-up studies of risk factors for the development of cancer in the same group of individuals.