Intracranial vessels are well innervated by both adrenergic and cholinergic nerves. They possess adrenergic and cholinergic receptors. A contractile response can be provoked by various amines, and noradrenaline can be released from the axons in the perivascular nerve plexus in amounts sufficient to induce strong vasoconstriction. The close relationship between adjacent perivascular cholinergic and adrenergic nerve terminals, also in the neuroeffector area, suggests axonal interaction. It is proposed that the autonomic innervation of brain vessels participates in the control not only of the cerebral circulation but also of associated intracranial pressure phenomena.