Among the tumor-associated antigens evaluated for the diagnosis and management of cancer, carcinoembryonic antigen (CEA) is the only established and clinically useful tumor marker for colorectal cancer and other CEA-producing tumors. Because of the exhaustive studies in the past decade, a consensus development conference was held at NIH in September 1980, to address the issue concerning the role of CEA as a marker in the management of cancer. This conference concluded that the use of regular and sequential assays of blood CEA is the best noninvasive technique for postoperative surveillance of patients to detect disseminated recurrence of colorectal cancer. The CEA level can serve as an indicator of successful or incomplete resection, and is useful in monitoring the effect of chemotherapy or radiotherapy. CEA can also provide a useful estimate of prognosis. CEA is neither sensitive nor specific enough to be used in routine screening for possible malignancy in an asymptomatic population. Nor can this test independently establish a diagnosis of cancer, but it can be used as an adjunct to clinical staging methods in known cancer patients. Radioimmunodetection and radioimmunotherapy with anti-CEA antibodies are currently being evaluated. Study of the pathophysiology and metabolism of CEA is needed. CEA remains the prototype tumor marker and is a valuable comparative tool, when investigating the clinical value of other newly developed tests for tumor markers.