The prognostic value of serum CA-125 levels both before chemotherapy and after each cycle of one or two courses was assessed in 48 patients with advanced ovarian adenocarcinoma. All patients received a minimum of six courses of either cyclophosphamide and cisplatinum (CP) or cyclophosphamide, doxorubicin and cisplatinum (CAP). Patients with serum CA-125 values below the normal value of 35 U/ml after two courses had a significantly longer median survival (p < 0.0001) and longer disease-free survival (p = 0.007) than did those patients whose CA-125 levels dropped to normal after the third or a later course of chemotherapy. A response in CA-125 levels after the first two courses of chemotherapy may indicate which patients should continue with the current chemotherapy regimen and which patients should be offered salvage therapy.