Delayed neurologic deterioration from vasospasm remains the greatest cause of morbidity and mortality following subarachnoid hemorrhage. The authors performed superficial temporal artery-middle cerebral artery bypass in three patients with symptomatic vasospasm and studied its effects on cerebral hemodynamics. All three patients responded neurologically to the bypass procedure within 24 hours. The average cerebral blood flow in the region supplied by the spastic middle cerebral artery increased from 40 ml/100 g/min to 49 ml/100 g/min after bypass. Angiography disclosed dilatation of donor vessels during the peak of spasm, followed by their decrease in caliber coincident with alleviation of vasospasm. The authors conclude that superficial temporal artery-middle cerebral artery anastomosis for the management of symptomatic vasospasm can increase blood flow in the ischemic region supplied by the spastic artery. This management strategy may lower the incidence of death and disability from vasospasm after subarachnoid hemorrhage.