Cerebral artery spasm following subarachnoid hemorrhage (SAH) is a major cause of morbidity and mortality. Treatment or prevention methods are most desirable. Using the basilar artery of the rabbit, cerebral arterial spasm was induced with an injection of 4 ml of autologous blood via cisternal puncture in six treated, four pre-treated and six control animals. Vertebral angiography was performed before and at ten, twenty, thirty and sixty minutes after the injection of blood was carried out, and the presence of spasm and its cause were followed in these animals. Pre-treated and treated subjects received 2 mg/kg of diltiazem (a calcium antagonist) either before and after the injection of blood, respectively. Analysis of vessel diameters by computer assisted densitometry showed that the treated group had a significant reduction of basilar artery spasm when compared to the control group, while in the pre-treated group, spasm was prevented.