To assess the predictive value of serum CA125 level prior to second-look laparotomy in epithelial ovarian carcinoma, 45 patients who were clinically or radiologically tumor-free prior to a second-look laparotomy were studied. Serum CA125 levels were measured 10 days prior to the operation, and were compared with the surgico-pathological results. Twenty-eight (62%) patients were found to have tumor at surgery. The serum CA125 levels were greater than or equal to 35 Uml(-1) (42%) patients. Tumors were found in 14 (74%) of these 19 patients. Although a serum CA125 level greater than or equal to 35 Uml(-1) was a strong predictor of the presence of an intraperitoneal tumor, a level < 35 U ml(-1) was not predictive of a tumor-free state. When the cut-off level was accepted as 20 U ml(-1), 28 patients (62%) were found to have elevated CA125 level. The sensitivity, the specificity, the positive and negative predictive value and the false negative ratio were calculated as 79%, 65%, 79%, 65% and 21% respectively. The threshold value for a raised CA125 level was considered and a lower level of 20 Uml(-1) was suggested as a cut-off level prior to second-look laparotomy in evaluating patients with known epithelial ovarian cancer.