The prognostic value of serum CA 125 measurements was assessed in 68 patients with epithelial ovarian cancer. All patients received a minimum of two courses of cisplatin at the Department of Obstetrics and Gynecology, Hanyang University Hospital. The end points of the analysis were surgically free of disease after completion of cytoreductive chemotherapy(pathological complete response: pCR) and 5-year survival rate. The positive rate of CA 125 was 78%(53/68) in patients with epithelial ovarian cancer. The prechemo-therapy level of CA 125(< or >35U/ml) was of value in predicting which patients would develop progressive disease(pCR: 100% vs 55%, 5-year survival: 100% vs 50%). We divided 53 cases( >35U/ml) into 4 groups according to CA 125 regression pattern as 1) absolute prechemotherapy CA 125 level(<100U/ml or >100U/ml), 2) sevenfold decrease after 1 month of chemotherapy(>1/7 or <1/7, 3) CA 125 level after 3 months(normal or abnormal), and 4) half life of CA 125(>20 days or <20 days). Pathological complete response rates were as follows 1) 100% vs 53%, 2) 75% vs 47%, 3) 50% vs 57%, 4) 55% vs 56%, respectively. 5-year survival rates were as follows : 1) 100% vs 41%(p= 0.004), Z) 67% vs 42%(p=0.033), 3) 50% vs 44%, 4) 57% vs 43%, respectively. In this study, absolute prechemotherapy CA 125 levels(100U/ml) and the change in CA 125 levels from before chemotherapy to 1 month later, after one course of cisplatin, could be used to divide patients into different prognostic groups in terms of survival rate. The change in CA 125 levels may indicate which patients should be offered alternative or symptomatic therapy and which should continue with the currently available toxic chemotherapy.