✓ This study reports the effects of intraarterial prostaglandin E1 (PGE1) upon intracerebral blood flow under control and vasospastic conditions. A new transorbital means of producing acute experimental subarachnoid hemorrhage with concomitant arterial spasm is presented. Two groups of animals were delineated in this investigation. Five animals (Group 1) were extremely sensitive to PGE1 and subarachnoid hemorrhage (SAH); carotid flow studies with simultaneous intracerebral angiography in this group demonstrated the ability of PGE1 to relieve vasospasm. Two other animals (Group 2) were relatively insensitive to SAH and PGE1. The study suggests an important role for PGE1 in the treatment of intracerebral vasospasm.