The cat basilar artery was exposed using the transclival approach. After administration of 5% ethanol via intravenous infusion, vasospasm was produced by applying the animal's fresh arterial blood to the exposed artery. The resultant vasospasm was of markedly reduced intensity and duration as compared to vasospasm in control animals. In ethanol-treated animals with spasm induced from non-autogenous fresh arterial blood free of ethanol, a reduction in the duration of vasospasm was noted although the initial intensity of spasm was similar to control animals. There was no anti-spasm effect if the ethanol infusion followed the production of vasospasm.