Between December 1983 and December 1988 we examined the postoperative tumor marker development and correlated this to the clinical course of the disease in 56 patients suffering from primary epithelial ovarian carcinoma of International Federation of Gynecology and Obstetrics stages I-III and with a preoperative CA-125 serum level less than or equal to 65 U/ml. In 54% of all cases there was a reduction of more than 50% of the CA-125 serum level within the first 3 months after surgery. Nine out of thirteen patients with progressive disease (69%) showed an increasing CA-125 serum level with a median lead time of 6 months (0-11 months) prior to clinical diagnosis. These preliminary results indicate that the monitoring of cancer patients with CA-125 tumor marker seems to be a useful method of early diagnosis of progressive disease even in patients with preoperative serum levels lower than 65 U/ml.