After acute interruption of cerebral blood flow, various hemodynamic, morphologic and metabolic changes ensue in the occluded area. Such changes and subsequent brain damage are of great concern in the course of temporary arterial occlusion during aneurysmal surgery. Many experimental studies investigating the processes of cerebral infarction have been done through selective occlusion of intracranial vessels, and it has been known that 4 to 8 minutes interruption of cerebral blood flow results in irreversible brain damage. Cerebral resistance following vascular occlusion may be influenced by collateral circulation, hypothermia and hyperventilation. Recently we experienced two patients with right middle cerebral artery aneurysms, who were operated upon under normothermia, slight hypotension, and hyperventilation using microsurgical technique. The technique of temporary occlusion of middle cerebral artery was applied as an adjunctive method.