Nitric oxide is a ubiquitous intercellular messenger involved in particular functions in the cardiovascular, immunological and nervous systems. In the cerebral cortex, nitric oxide is synthetized by endothelial cells and by a discrete population of neurons and glial cells expressing nitric oxide synthase. Nitric oxide of endothelial and neuronal origin is involved in the regulation of cerebral blood flow. In this review, we have tried to combine morphological data providing information on the chemical nature of nitric oxide synthase-containing neurons and their arrangement, especially in relation to intracortical blood vessels, with functional results suggesting the participation of these neurons in the coupling between local cortical blood flow and synaptic activity.