&NA;Forty‐six patients were followed with serial CEA determinations by two CEA assays after curative resection of a primary or recurrent colonic cancer. Thirteen have had a histologically proven recurrence, of which only six (46 percent) were predicted by both assays, while seven (54 percent) were predicted by one assay only. The assays appear complementary in indicating tumor recurrence, and preliminary findings suggest that it may be beneficial to follow patients with more than one CEA assay after resection of a primary or recurrent colonic cancer.