Systemic administration of the dopamine (DA) receptor agonist apomorphine leads to a general increase in cerebral blood flow (CBF) as determined by the autoradiographic iodoantipyrine technique. The magnitude of the increase varies between different regions but shows no obvious relation to the density of either DA terminals or receptors. The circulatory response is much more prominent in the lateral than in the medial caudate-putamen. Apomorphine seems to increase CBF both via a change in metabolic rate and via stimulation of dilatory vascular receptors. In animals with unilateral 6-hydroxydopamine lesions of the ascending DA pathways apomorphine induces an augmented CBF response in some denervated structures, notably caudate-putamen and globus pallidus. It is concluded that this is partly due to stimulation of denervated supersensitive vascular receptors, suggesting a direct dopaminergic control of the blood vessels in these areas.