Outpatient follow-up in patients operated upon due to carcinoma of the colon and rectum is usually performed, due to a high rate of recurrence and with the aim of finding a curable recurrence. Due to the enormous cost of an extended follow-up system, a careful evaluation of the benefit is needed. The aim of the present investigation was to study the efficacy of the different tools in an extended follow-up. One hundred ninety patients with carcinoma of the colon and rectum were-apart from traditional clinical follow-up-followed with an extensive laboratory battery including carcinoembryonic antigen (CEA), erythrocyte sedimentation rate (ESR), hemoglobin (Hb), electrophoresis, ALP, and GT. Forty-seven recurrences were found. Thirty-one of these recurrences were first detected by a rise in CEA. Seven cases were detected at clinical follow-up and six cases due to symptoms suggestive of recurrence. The predictive value of a positive test was 79.4% for CEA but very low for the other tests studied. A negative value for any of the tests in the battery was usually accurate. Follow-up after colorectal carcinoma should include CEA as the only laboratory parameter. Postoperative colonoscopy for removal of missed synchronous lesions, chest X-ray, and endoscopic investigations of the anastornotic region also seem to be of value.