At present, it is known that a connection exists between neuronal activity and microvascular blood flow and permeability in the CNS. We have demonstrated the presence of immunoreactivities against both GABA and GAD as well in the endothelial capillary cells of rat cerebellar cortex, as in perivascular glia, neuronal bodies, dendrites and axon endings, in close association with the basal membrane of the pericyte or endothelial cells. These results support the suggestions from biochemical and pharmacological studies about the relationship between GABA and microvascular function in the CNS.