The author studied the immunohistochemical localization of alpha and beta subunits of S-100 protein in normal human cerebral and glioblastoma tissues by an indirect immunoperoxidase method. The glial cells including astrocytes and oligodendrocytes showed positive staining for both alpha and beta subunits of S-100 protein, however, the neurons revealed positive staining for alpha subunit only. The positive staining for both alpha and beta subunits of S-100 protein was revealed in one case of 6 glioblastomas examined and the positive staining for either alpha or beta subunit in three cases. The other 2 cases showed no positive staining. By immunoelectron microscopy, the glial cells revealed positive reaction product for both alpha and beta subunits of S-100 protein throughout the cytoplasm. Occasionally, the positive reaction products for both alpha and beta subunits were observed in the glial nucleoplasm and outer membrane of cell organelles including rough endoplasmic reticulum. The subcellular localization of alpha subunit of S-100 protein in the neurons and glioblastoma cells is basically simillar to that of the glial cells. The immunoelectron microscopic study of the subcellular localization of S-100 protein subunits seems to be one of the useful methods in assuming the biological role of S-100 protein.