Indirect immunoperoxidase staining by the peroxidase-antiperoxidase (PAP) technique was carried out on 23 human primary intracranial germ-cell tumors (17 germinomas, one embryonal carcinoma, one yolk-sac tumor, three teratomas, and one teratoma with embryonal carcinoma) and on six human primary pineal non-germ-cell tumors (one pineocytoma, two pineoblastomas, two astrocytomas, and one glioblastoma multiforme). The technique used specific rabbit antisera against placental alkaline phosphatase (PLAP), alpha-fetoprotein (AFP), and human chorionic gonadotropin (HCG). Thirteen of 17 intracranial germinomas (76.5%) showed positive staining for PLAP mainly on the tumor cell membrane. In six primary intracranial non-seminomatous germ-cell tumors, there was weak positive staining indicating the presence of PLAP in only a few cells of one embryonal carcinoma, and in some glandular epithelial cells of one teratoma; this staining was limited to the cytoplasm. None of the other six primary pineal non-germ-cell tumors showed any positive PLAP reaction. From these results, PLAP was shown to be very useful in histopathology as a diagnostic tumor marker of intracranial germinoma. Positive AFP staining was seen in several yolk-sac tumor cells and a few embryonal carcinoma cells. However, no intracranial germinomas and non-germ-cell tumors of the pineal region showed positive reaction. As for HCG, only one suprasellar germinoma and one pineal embryonal carcinoma among 29 specimens contained a few positive-staining tumor cells.