The prognostic significance of CA 125 half-life in patients with ovarian cancer who have received primary chemotherapy after surgical cytoreduction. Fifty-four patients with advanced epithelial ovarian cancer were monitored with serial serum CA 125 levels after surgical cytoreduction and during multi-agent chemotherapy with cisplatin-containing regimens. CA 125 half-life of less than 20 days was associated with prolonged overall survival (p less than 0.015). In those patients who eventually were found to be disease-free at surgical surveillance procedures, normalization of serum CA 125 levels to less than 35 U/ml within 65 days of primary operation also suggested an improved survival (p less than 0.059). 