Carcinoembryonic antigen is elevated in the plasma of approximately 30% of patients with endometrial adenocarcinoma, 50% of patients with ovarian carcinoma, and 60% of patients with cervical carcinoma. The incidence of elevated plasma CEA is directly related to stage of disease, and in ovarian cancer to cell type. Immunodiffusion and immunoelectrophoretic studies have indicated that CEA from ovarian and cervical cancers is similar to colonic cancer CEA. Tumor staining for CEA by the immunoperoxidase method (indicating a CEA concentration of greater than or equal to 3.0 microgram/g tissue) is positive in about one-half of the patients with elevated plasma CEA levels. However, there is no definite relationship between tumor and plasma antigen levels. Carcinoembryonic antigen levels charcteristically return to normal within 8 weeks following complete surgical removal of tumor. In contrast, antigenemia often persists up to 4 months following curative radiation therapy. A progressive rise in plasma CEA has preceded clinical diagnosis of recurrence in about half of the patients studied. Serial plasma CEA determinations in patients whose plasma or tumors initially contain elevated amounts of antigen provides information concerning the biologic behavior of malignancy which may be of clinical significance to the patient.