Two hundred asymptomatic United States veterans older than 40 years of age were evaluated with a flexible sigmoidoscope plus Hemoccult stool tests. Mean distance and time for the former were 56.4 centimeters and 7.4 minutes, respectively. There were no complications. Polyps greater than or equal to 0.5 centimeter in diameter were found in 11.9 per cent of those older than 50 years. No polyps of this size were found in patients younger than 50 year of age. Results of Hemoccult tests were negative in 83.3 per cent of those with polyps. A flexible sigmoidoscope is a safe, rapid and effective means of identifying that portion of the asymptomatic adult population having colonic polyps. For this purpose, it is vastly more sensitive than Hemoccult stool testing. Because of the relationship between colonic polyps and carcinoma, this technique may prove invaluable in the identification of those patients with an increased potential for the development of carcinoma of the colon.