Results are reported of a 5 year trial with the Haemoccult stool-test in a diagnostic center (DKD), and of a 1 year trial in the offices of 110 physicians. In the DKD 8 000 patients were tested: In a non-selected group 2,4% and in a selected one 3,8% of tests performed turned out to be positive; the diagnosis of carcinoma of the colon or rectum was established in 32 of these cases and 45 large polyps were traced. In most of the offices the test was positive in less than 3% of the patients tested, 57 of these patients had a carcinoma and 26 polyps. In 54 of all 89 cases with carcinoma and in 46 out of 71 polyps the lesions could not be found by digital or rectoscopic examination, due to a higher localization; 17 of the cancer patients were asymptomatic except for a positive Haemoccult test. Using only 3 tests per patients, 7 out of 96 colorectal cancers and 27 out of 98 large polyps were negative. 6 haemoccult tests to be done on three successive stools (as originally proposed by Greegor) are recommended as a yearly routine procedure in all persons about 40 years of age for early detection of carcinoma or polyps of the colon.