Study was made of a kindred with a strong history of carcinoma of the colon. Twenty-three family members were screened for the tumor with carcinoembryonic antigen (CEA) assay, barium enema, and proctoscopy; one occult colon cancer was diagnosed. Identification and surveillance of families at high colon cancer was diagnosed. Identification and surveillance of families at high risk of cancer can provide unusual opportunities for early tumor detection.