Serum carcinoembryonic antigen (CEA) tests were performed on 36 patients with histologically proved locally recurrent or residual malignant disease after resection of colorectal carcinoma but with no clinical evidence of distant metastasis. Only nine patients (25%) had abnormal CEA levels of greater than 5 ng/ml despite the fact that most patients had had symptoms of recurrence for several months. Among the nine of our patients, none had CEA values greater than 5 ng/ml, and only three had levels greater than 2.5 ng/ml (3.4, 3.8, and 4.7 ng/ml). The CEA assay is not a sensitive test for early detection of recurrence of colorectal carcinoma.