CA 125 serum levels were measured in 74 patients with ovarian carcinoma. Among 31 patients undergoing a second look laparotomy (SL) after chemotherapy pathologic complete response (PCR) was observed in 14 patients, residual disease (RD) less than 2 cm in 7 patients and RD greater than 2 cm in 10 patients. The disease status was compared to the CA 125 serum levels measured just before SL. Thirteen of the 14 patients with PCR had serum CA 125 values less than 35 U/ml (specificity: 93%). On the other hand, only 10 of the 17 patients with RD showed serum levels greater than 35 U/ml (sensitivity: 59%). Moreover, in the 43 patients receiving chemotherapy, CA 125 levels correlated with the course of the disease in 36 (84%). With regard to early detection of recurrence, in 9/14 patients with PCR, whose CA 125 levels were monitored monthly, by 1 to 7 months an increase of the tumor marker preceded clinical evidence of relapse in 9/9 relapses (100%). In conclusion, CA 125 assay can be helpful in the management of ovarian cancer patients, in monitoring the response to chemotherapy, in the early detection of tumor recurrence, and in predicting the SL findings, although the low sensitivity could be a major drawback in patients with RD before SL.