Serum from 161 patients with ovarian cancer, 28 patients with benign gynecologic disorders and 22 healthy women, was assayed for levels of tumor marker LSA, which were compared with CA125. The results showed that in the patients with ovarian cancer, the sensitivities of LSA and CA125 for the patients prior to surgery were 83.0% and 92.5%, respectively; the sensitivities for the recurrent patients after surgery were 73.7% and 82.5% respectively. A total sensitivity of 89.5% was obtained by combination of both markers. The positive predictive value of LSA and CA125 for the patients with suspected tumor recurrence were 89.4% and 100%, respectively, and their corroborative rate with the postoperative courses were 94.4% and 100%, respectively. Thus serum assay of LSA, can be used in monitoring patients with ovarian cancer. The technique for determination of serum level of LSA is much more simple and less expensive than the radioimmuno-assay of serum level of CA125.