Fecal Hemoccult testing and flexible sigmoidoscopy have been proposed as means of screening for colorectal cancer in the general population, as well as in identified high-risk groups. A colorectal cancer screening program was conducted for the Pattern Makers' League of North America. A total of 1,473 white males were screened with fecal Hemoccult testing and flexible sigmoidoscopy during the period 1981 to 1983. The fecal Hemoccult test after diet restriction was positive in 38 workers (3.6%). Among 12 colorectal cancers, including in situ cases, only three were positive by this test. The sensitivity of this test for picking up cancer is only 25%. The positive predictive value was 7.9%. It is concluded that the Hemoccult test for the detection of colorectal cancer and polyps is not a valuable tool because of low sensitivity, whereas flexible sigmoidoscopy has a significant role in colorectal cancer screening of an asymptomatic population at risk.