Serum levels of CA-125, CA-15-3 and TAG-72 were measured in 81 patients with endometriosis, diagnosed by laparoscopy, and staged according to the Revised American Fertility Society, and in 31 control subjects. The values of CA-125 and CA-15-3 were also determined in peritoneal fluid. The aim of the present study was to evaluate the clinical usefulness of these various markers in the diagnosis of endometriosis by using them either by themselves or combined. High serum levels of CA-125 were found in 43 of 81 patients with endometriosis (53%) and in five of 38 control subjects (13%). The values of serum CA-125 progressively increased in relation to the severity of the disease. High serum values of CA-15-3 and TAG-72 were also found in patients with endometriosis, but with a similar incidence also in control patients. High CA-125 and CA-15-3 values in peritoneal fluid were found in all patients investigated. These results suggest that measurement of serum CA-15-3 and TAG-72 in addition to CA-125, does not provide any advantage for the diagnosis of endometriosis.