We carried out the ultracytochemical study of Ca(2+)-ATPase activity for the developing rat brain at embryonic day 11 (E 11), E 14, E 19 and postnatal day 5(P 5), and for the adult rat cerebrum. Matrix cells at E 11 and neuroblasts at E 14 showed no cytochemical reaction (CR) for Ca(2+)-ATPase activity. Glioblasts at E 19 showed very weak CR. Reaction product (RP) was observed on the surfaces of the neuronal and glial cells at P 5 and adult rat cerebrum. Microvessels at E 14 demonstrated no CR, but microvessels at E 19 showed CR, in which RP was, of a fine granular appearance, diffusely observed along the luminal and abluminal surfaces. At P 5, coarsened RP was diffusely observed on the luminal and abluminal surfaces. The CR for capillary Ca(2+)-ATPase activity in the adult rat cerebrum was found to be mild and the RP formed continuous and discontinuous thin layer on the abluminal surface. The results suggest that Ca(2+)-ATPase activity is closely related with development of the cells in the central nervous system.