Serial serum CA-125 levels were measured in fifteen patients with recurrent or advanced endometrial carcinoma during treatment with chemo- or hormonal therapy. All patients had measurable disease by physical examination, chest X-ray or CT scan. Serum CA-125 levels were invariably elevated, and generally reflected, response to therapy in all patients with intraperitoneal or pulmonary metastases. Levels were normal in two of three patients with isolated vaginal metastases prior to and following response to progesterone.