Membrane-bound Ca2(+)-ATPase activity was localized cytochemically in the blood vessels of the spinal cord of rat embryos to obtain a better understanding of the membrane activities of vascular cells. The cytochemical method revealed a growth of the parenchymal vasculature. In the parenchyma, reaction product was dense over the entire plasma membrane of voluminous endothelial cells provided with large nuclei and enriched cytoplasmic organelles, suggesting that the endothelial cells may be of a vascular sprout. The parenchymal vessels with a wide lumen were frequently associated with pericytes, and the Ca2(+)-ATPase activity was diminished in intensity on the luminal surface of the flattened endothelial cells. On the other hand, the endothelium of extraparenchymal capillaries exhibited Ca2(+)-ATPase activity primarily on the luminal surface of the plasma membrane. Quercetin, a Ca2(+)-transporting ATPase inhibitor, considerably decreased the abluminal activity in the voluminous endothelial cells with slit-like vascular lumen and the luminal activity of functioning capillary endothelium as well. Thus, a dual activity of Ca2(+)-ATPase, postulating for the activities of Ca2(+)-transporting ATPase and ecto-ATPase, was closely correlated with the maturation processes of the capillary endothelium.