Preoperative serum levels of CA125 and tumor-associated trypsin inhibitor (TATI) were measured in 220 patients undergoing laparotomy for adnexal masses. Of the 57 patients with epithelial ovarian cancer. 86% had serum CA125 higher than 35 kU/l and 81% higher than 65 kU/l while 51% had serum TATI above 22 micrograms/l. In eight patients with mucinous ovarian malignancies, serum levels of CA125 were above 65 kU/l in 6 cases while serum TATI was above 22 micrograms/l in 4 cases. Of the 163 patients with benign ovarian masses, 41% had serum CA125 levels above 65 kU/l and 17% above 65 kU/l whereas serum TATI was above 22 micrograms/l in 6%. In 11 cancer patients having elevated levels of both CA125 and TATI at diagnosis, the serum concentrations of these antigens were periodically measured during and after treatment. Changes in CA125 and TATI levels correlated with the clinical course in 84% and 37% of the instances, respectively. After the sixth course of chemotherapy, the diagnostic accuracy of the markers in the evaluation of the disease status at second-look laparotomy was 55% for CA125 with a cut-off level of 35 kU/l, 36% for a cut-off level of 65 kU/l, 55% for TATI, and 66% for the combination of CA125 and TATI with cut-off levels of 65 kU/l and 22 micrograms/l. CA125 is the most sensitive marker for epithelial ovarian cancer, but the concomitant measurement of TATI could be of benefit in both differential diagnosis of adnexal masses and monitoring of response of epithelial ovarian cancer to treatment.