A histochemical study on alkaline phosphatase, acid phosphatase, β-esterase, β-glucuronidase, lactic dehydrogenase, glucose-6-phosphate dehydrogenase, succinic dehydrogenase, malic dehydrogenase, isocitric dehydrogenase, glutamic dehydrogenase, α-glycerophosphate dehydrogenase and β-hydroxybutyric dehydrogenase has been carried out to clarify the relationship between the clinical feature and the enzyme activities of brain tumors. The materials used in this study were human brain tumors removed from 140 patients in our department from June 1962 to April, 1966. Two-thirds of these specimens were kept at 20℃. immediately after the removal, the rests were quickly frozen by ice aceton mixture, and serially cut at 20μ thick in a -20℃. cryostat, then the sections were incubated in each histochemical reaction mixture. For the histochemical demonstration of hydrolytic enzymes, azo-coupling method was employed, and for the oxidative enzymes, the method described by Pearse was employed. The following results were obtained; 1) In gliomas the cells of astrocytoma grade 1 showed a marked reaction of alkaline phosphatase activity, but decreased in poorly differentiated gliomas. 2) In too-thirds of the cases with gliomas, the longer the duration of clinical symptoms and singns, the more benign were the histological pictures and the stronger in alkaline phosphatase activity. 3) Other enzymes activities in gliomas showed not any specific reaction with the tumors and the prognosis. 4) Alkaline phosphatase, leucine aminopeptidase and acid phosphatase activities are remarkable in fibroblastic meningioma, moderate or feeble in meningocytic meningioma, and negative in malignant meningioma. Other enzyme activities in meningiomas showed no specific features. 5) Acoustic neurinomas show moderate or lower activities of hydrolytic and oxydative enzymes, and there is no characteristic feature on histochemistry.