A screening program for colorectal cancer and adenomas has been applied to 6,579 mostly asymptomatic men and women age 40 years and older utilizing fecal occult-blood testing followed by investigation of patients with positive slides by air-contrast barium enema and colonoscopy. A control population of 7,325 patients had sigmoidoscopy only and no occult-blood testing. Approximately 1% of the patients had positive slides; most patients had only one or two slides positive. Approximately 50% of patients with positive slides had significant neoplastic lesions, including 23 patients with large adenomas and 7 patients with cancers. Pathological staging of cancers was more favorable in the screened asymptomatic group as compared with the control group. Neoplastic lesions seen on sigmoidoscopy in screened patients who had negative fecal occult-blood tests included 2 cancers and 15 large adenomas. Reasons for false negativity include possible conversion of initially positive slides to negative. Screening for colorectal cancer and adenomas with fecal occult-blood testing appears to be feasible approach with good patient compliance, and manageable rate of positive slides productive of a high percentage of neoplastic lesions. The number of false-positives seems to be low. False negativity has been observed and will require further study.