Four hundred patients with resectable colon and rectal cancers were operated on by 37 surgeons at 31 institutions. Patients were monitored with carcinoembryonic antigen (CEA) level determinations and clinical examinations. One hundred thirty patients had recurrences, and 75 were reoperated on, with 43 reoperations CEA-directed and 32 clinically directed. Two of 75 died within 1 month after the second operation. Twenty-two second-look patients remain free of disease 5 years after their second operaton. The highest resectability of recurrent cancer occurred in patients with a CEA level below 11 ng/ml in whom the CEA level was determined at intervals of 1 to 2 months. Cancer 55:1284-1290, 1985.