In attempt to identify patients with ovarian carcinoma and differentiate them from patients with benign ovarian tumor or other gynecological malignancies, peritoneal fluid and serum lactate dehydrogenase (LDH) levels were measured in 51 patients: 15 with ovarian carcinoma, 15 with endometrial carcinoma, 4 with cervical carcinoma, and 17 with benign ovarian tumor. Peritoneal fluid and serum LDH levels in ovarian cancer patients were significantly higher than those in patients with benign ovarian tumor (P < 0.001) or other gynecological malignancies (P < 0.001 and P < 0.03, respectively). Yet, peritoneal fluid LDH demonstrated higher diagnostic sensitivity (87%) and greater diagnostic accuracy (90%) than serum LDH (60 and 77%, respectively) or serum CA-125 (73 and 83%, respectively). Comparing the histological types of ovarian cancer, serous cystadenocarcinoma presented higher peritoneal fluid LDH levels than endometrioid or mucinous cystadenocarcinoma. No difference in peritoneal fluid LDH was observed comparing different stages of ovarian cancer. The results suggest that peritoneal fluid LDH may be an efficient biochemical marker in diagnosis of ovarian cancer.