This study reports the effect of intracisternal administration of papaverine in 15 patients with vasospasm due to rupture of aneurysm. All patients had undergone clipping of aneurysm and had neurological deterioration and decreasing level of consciousness. Bolus injection of 40 mg of 1% papaverine hydrochloride was started on day 6.3 +/- 1.7 and continued for 4.4 +/- 1.6 days. In seven cases serial angiogram after initial dose revealed dilatation of IC and/or anterior, middle cerebral arteries at 30 min and further dilatation up to 85% increase in diameter at 60 min, which continued at least 90 min. Arteries with marked vasospasm responded more to papaverine than those with less vasospasm. There was a close correlation between degree of vasospasm and vasodilatation effect (r = 0.88, p less than 0.01). In all but two cases vasodilatation tended to become prominent by repeat doses, twice a day, for two to seven days (r = 0.87, p less than 0.01). Vasodilatation was observed only in IC and proximal trunks of ACA and MCA where papaverine could make direct contact, but not in the distal branches beyond A3 or M3. Neurological examination showed improvement of paresis or level of consciousness in 7 cases but no effect in 6 cases. Intracerebral hematoma occurred in two cases (one by high concentration 4% papaverine) during the treatment. Therefore intracisternal papaverine is the treatment of choice in cases with symptomatic vasospasm with some cautions on concentration to be administered.