Cancer antigen-125 (CA-125) is a sensitive, but not a specific, tumor marker used for the diagnosis and monitoring the efficiency of therapy in patients with epithelial ovarian cancer. Many studies have been published concerning the efficiency of CA-125 in patients with epithelial ovarian carcinoma. However, the effects of ovarian mass volume, ascites amounts and peritoneal carcinomatosis on serum CA-125 have not been completely understood. For this reason, this study was planned to investigate the effects of ascites, ovarian mass volume and peritoneal carcinomatosis on serum CA-125 levels, and a series of 98 patients with stage I-IV nonmucinous epithelial ovarian carcinoma was enrolled for the Study. Amounts of ascites were determined in each patient with ascites. Ovarian mass volumes were calculated in 22 patients with stage I disease without ascites. Peritoneal carcinomatosis was detected in 35 ovarian cancer patients. Serum CA-125 levels were compared among the patients with different clinical conditions.