&NA;Utilizing a double subarachnoid blood injection model in pigs, we have evaluated the protective effect of the intracisternal injection of the thrombolytic agent, plasmin, in preventing the secondary intracranial arteriopathy seen after artificial subarachnoid hemorrhage in untreated animals. Twelve animals injected with plasmin revealed markedly less intimal proliferation and medial necrosis than were seen in control animals. These observations support the hypothesis that the persistence of clotted blood around the intracranial arteries is the cause of the vasculopathy. (Neurosurgery19:20‐25, 1986)