Serum CA 125 (an antigen common to most nonmucinous epithelial ovarian carcinoma) were measured in patients with gynecologic disease. CA 125 levels were elevated (34U/ml or higher) in 77.8% (7/9) of ovarian cancer patients. As the CA 125 levels correlated well with the clinical course, we conclude that the measurement of serum CA 125 is useful for the diagnosis and follow up of patients with ovarian cancer.