Alkaline phosphatase (ALPase) and Mg2+-activated ATPase (Mg2+-ATPase) activities were demonstrated in human brain tumors by light and electron microscopy. Four cases of glioma, i.e., two cases of astrocytoma, grade II, and two cases of glioblastoma, were used as materials. At the light microscopic level, Mg2+-ATPase activity was observed in the capillary wall and glial cells of both astrocytoma and glioblastoma. ALPase activity was restricted to the capillary wall. Its activity was stronger in glioblastoma than in astrocytoma. By electron microscopy, in astrocytoma, reaction product representing Mg2+-ATPase activity was distributed in the plasma membranes of endothelial cells and pericytes. Activity was primarily localized at the abluminal surface of endothelial cells and the surface of pericytes facing endothelium. The plasma membrane of glial cells was also positive. ALPase activity revealed essentially the same distribution pattern in blood vessels as above. In glioblastoma, on the other hand, activities of both phosphatases were markedly positive on the luminal surface of the plasma membrane of endothelial cells. They were much stronger than those along the abluminal endothelial surface. Phosphatase activities in brain tumor appear to change in localization pattern in association with glioma malignancy. This might reflect a functional aspect of changes in blood-brain barrier in glioma.