Determination of carcinoembryonic antigen (CEA) in serum has been performed in 253 patients with proved adenocarcinoma in the colon and rectum. Preoperative CEA was normal in 58.3% of the patients. A correlation between CEA level and Dukes' grading was found. There was, however, no statistically significant difference in recurrence rate between patients with normal and patients with elevated pre-operative CEA. Transient CEA elevation was seen in the follow-up period after curative resection in 21.8%. 75% of the patients with recurrence had abnormal CEA, and CEA elevation was the first sign of recurrence in 59.1%. The majority of these patients, however, had advanced disease not available for surgical treatment. In cases with local resectable tumour CEA often was normal. Only a few patients had advantage of CEA determination for diagnosis of recurrence and its routine use is therefore questioned.