In 1987/88 and 1988/89 we tested the population (aged greater than or equal to 40) of the district of Oberpullendorf in 2 series for faecal occult blood by means of the Hemdetect Test. In the first test series the test was offered to 18,233 persons and 8235 (45%) persons completed the test; 187 (2.3%) were positive. In the second series 6512 (36%) out of 18,241 completed the test and 472 (7.2%) persons were positive. The persons with positive results were examined by colonoscopy, gastroscopy, and abdominal sonography, in combination with routine investigations. Secondary compliance in these investigations was 92%. The screening method revealed 34 colorectal cancers with the favourable pathological staging: Dukes A 18 (53%), Dukes B 6 (18%), Dukes C 10 (29%), Dukes D 0. 11 polyps showing carcinoma in situ and 174 polyps (70% of which were adenomas) in 124 patients were treated by colonoscopy. In the meantime we have detected 14 "interval" cancers among people with a false negative test result, also at a favourable staging: Dukes A 6 (43%), Dukes B 4 (29%), Dukes C 4 (29%), Dukes D 0. In the non-responders we found 30 colorectal cancers at a much worse staging: Dukes A 7 (23%), Dukes B 10 (33%), Dukes C 8 (27%), and Dukes D 5 (17%). Screening for faecal occult blood in combination with the necessary investigations of the positive persons by colonoscopy is able to detect symptomless colorectal cancers at a less advanced pathological stage and enables the treatment of precancerous adenomatous polyps. An improvement in cumulative sensitivity is expected on annual repetition of screening for faecal occult blood.