Serial CEA levels have been studied preoperatively, and one day, 10--15 days, four months, and eight months after surgery in a group of colon cancer patients who started soon after surgery a protocol of adjuvant immuno(chemo)therapy with Levamisole R and BCG R. Results showed a decrease of mean values of plasma CEA levels from preoperatively to four months after surgery, while eight months after surgery a slight increase was noted. Some of the patients in whom disease recurred showed persistent high levels of CEA, while one patient was consistently a false-negative notwithstanding a bone recurrence. While the prognostic value of serial CEA determinations is confirmed, the possibility of restarting (or intensifying) a protocol of adjuvant immunochemotherapy given high CEA levels and a negative clinical picture is discussed.