Plasma carcinoembryonic antigen (CEA) levels in 75 patients with invasive cervical cancer were measured during and after radiation therapy. Initial CEA levels were elevated in 65% of the patients, the incidence varying with stage of disease. Of the 32 patients followed during therapy, CEA levels rose in 26 (81%). CEA values after therapy in the same 32 patients showed three patterns: (1) decline to normal, associated with a disease-free state; (2) decline but not to normal, associated with heavy cigarette smoking or persistent disease; and (3) decline to normal, followed by a rise to abnormal, associated with tumor recurrence. Elevation of CEA levels preceded recognition of recurrent cervical cancer by as much as 4 months in five of seven patients.