The prognostic significance of serum CA 125 level measured in the week before second-look operation was evaluated in 208 patients with invasive epithelial ovarian cancer. Serum CA 125 level was greater than 35 U/ml in 44.7% of patients. All patients with pathological complete response (PCR) had a serum CA 125 level less than or equal to 35 U/ml except one who developed lung metastases 2 months later. The sensitivity of serum CA 125 for identifying residual tumor at second-look operations was 58%, the specificity was 98%, the predictive value of a positive test was 99%, and the predictive value of a negative test was 43%. By Cox regression analysis, tumor state of second look, serum CA 125 level, histologic type, FIGO stage, and tumor grade were identified as independent prognostic factors for survival. We conclude that measurement of serum CA 125 level after induction chemotherapy represents a noninvasive method to identify patients at high risk for subsequent death from ovarian cancer. As far as we know, this is the first report to identify serum CA 125 level as an independent prognostic factor at the time of second-look laparotomy.