Abstract An innovative screening program for the detection of colorectal cancer was conducted in a county of 300,000. In fifteen centers a free rectal examination was offered and each participant received a kit with dietary instructions and three stool guaiac test slides to be returned by mail. The project was based on a study suggesting that bleeding from early tumors can be effected by a high roughage, irritating diet. False-positive results are reduced by eliminating meat, fish, and chicken from the diet. In a single day 3,450 people registered for the test. Of these, 2,625 returned the test slides and 159 had a positive reaction for blood. Five persons were discovered to have cancer and treated; all had been asymptomatic at the time of the screening test. Three of these patients are now probably cured. As an effort in mass education, the project appeared highly successful and was well received. As an accurate method for screening, it cannot be determined whether significant disease was over-looked; however, despite its obvious defects the program detected twice the number of cancerous lesions expected. We strongly urge the use of sequential guaiac testing with dietary preparation both as a mass screening effort and as a routine office procedure. It should be easy to give each patient a packet of test slides with dietary instructions either at the time of the annual office visit or in advance of it. This will add another parameter to determining how extensively to pursue investigation of the gastrointestinal tract and may lead to the discovery of many unsuspected and hopefully curable cancerous lesions.