PIP: Clinical research was carried out to determine the efficiency of PGE1 (prostaglandin E1) as a spasmolytic agent on cerebral vasospasm after subarachnoid bleeding. PGE1, ranging in dosage from .000002 ug/kg/min-.03 ug/kg/min., was injected into the internal carotid artery of 3 male and 3 female subjects suffering from subarachnoid bleeding due, in most of the cases, to arterial aneurysm. A 10-fold higher dosage concentration was used if repeat injection was required. Arterial diameter, circulation time and cerebral blood flow were measured. Blood pressure, respiration, and electrocardiographic changes were monitored. No definite spasmolytic effects were observed. No major adverse reactions were recorded. The clinical condition of 5 of the subjects was not changed after PGE1 infusion. The 6th case improved briefly after a few hours postinjection. Dosages in the study were small. The question remains as to whether the vasoactive effect of PGE1 is due to direct inhibition of the catecholamine effect on vascular smooth muscle or due to an unrelated vasodilator effect of PGE1.