Serum placental alkaline phosphatase (PLAP) levels in patients with gynecological tumors were measured by two kinds of enzyme-antigen immunoassay kits provided by Innogenetics (PLAP-I) and Sangtec Medical (PLAP-S), and the combination assays for PLAP with other tumor markers were studied. None of the healthy women studied were PLAP positive, and the positive rate in patients with benign ovarian tumors was less than 6%. The positive rate in patients with ovarian cancers was about 35%, which was higher than the rates for other cancers. It was significantly higher in patients with ovarian serous cystadenocarcinoma (60%). Remarkably high PLAP-I values were observed in patients with dysgerminoma. By the combination assay for PLAP with CA54/61 antigen in ovarian cancers, the diagnostic efficiency increased compared with that for PLAP and CA125. We conclude that PLAP is useful in the diagnosis of ovarian serous cystadenocarcinoma and dysgerminoma and that CA54/61 is the better partner for the combination assay.