To examine the cellular localization of each inhibin subunit in hydatidiform mole and invasive mole.Tissues were collected and fixed in Bouin's solution and studied with the immunohistochemical technique avidin-biotin-peroxidase complex.In the villous trophoblasts of hydatidiform mole and invasive mole, distinct immunostaining for inhibin alpha-subunit was observed in proliferative syncytiotrophoblasts, but not in the cytotrophoblasts. Positive immunostaining for beta A- and beta B-subunits was observed in both syncytiotrophoblasts and cytotrophoblasts. In extravillous trophoblasts of the invasive mole, staining for beta A- and beta B-subunits was observed, whereas staining for alpha-subunit was not detected.Inhibin-activin subunits may be produced in the trophoblasts of hydatidiform mole and invasive mole, and inhibin and activin may play a role in trophoblastic proliferation and invasion.