Serum CA 125 levels were measured preoperatively in 100 women undergoing diagnostic laparotomy for palpable adnexal masses. All 11 patients with frankly malignant nonmucinous ovarian carcinoma had serum CA 125 levels greater than 35 U/mL and nine of the 11 had serum CA 125 levels greater than 65 U/mL. If patients with mucinous and borderline lesions were included, serum CA 125 was greater than 35 U/mL in 11 of 18 and greater than 65 U/mL in nine of 18 patients. Among 14 individuals with pelvic masses and CA 125 greater than 65 U/mL, 13 had some form of gynecologic malignancy. These results suggest that CA 125 assay can be used as a diagnostic adjunct for discriminating benign from malignant pelvic masses.