Occult blood test for the screening of colon cancer has been made by immunological method using tatex agglutination for 4 years since 1988. A total of 35,139 persons have received the screening test and out of 1886 persons, that is, 5.4% showed positive. Five hundred seventy of the positive result subjects (30.2%) underwent barium enema examination. Three hundred fifty nine subjects (62.8%) showed some abnormal findings. They underwent colonoscopic examination and 45 of them (7.9%) had colon cancer. Twenty six of these were of early stage type and 19 persons were of advanced stage.