Cerebral vasospasm (V.S.P.) is a major complication of subarachnoid hemorrhage. In order to investigate this cerebral vasospasm, an intracisternal injection of autologous blood and topical application around the internal carotid artery was performed in the dog model. Thirty dogs were divided into five groups and a cerebral angiography was performed on D0, D2, D5, D7 and D9. In comparison with the control group (group 1), the angiography in group 2 (12 dogs) systematically exhibited severe V.S.P. In group 3 (intracisternal injection of venous blood: 5 dogs), the angiography exhibited no vasospasm at all. In group 4, a left frontoparietal flap was opened, allowing us to deposit blood around the carotid bifurcation. In these cases, a severe narrowing of cortical arteries was demonstrated. In group 5 (intracisternal injection of heparinated blood), no vasospasm was observed. These findings suggest that the vasospasm involves the circle of Willis' as well as the cortical arteries.