In 58 patients with progressive neurological deterioration from angiographically confirmed cerebral vasospasm after spontaneous subarachnoid hemorrhage, arterial hypertension was induced in an attempt to improve their deficits. The most effective regimen consisted of intravascular volume expansion, blockade of the vagal depressor response, and the administration of antidiuretics and vasopressor agents. With this protocol, arterial blood pressure could be sustained at high levels for prolonged periods. Neurological deterioration was reversed in 47 patients, transiently in 4; permanent improvement occurred in 43. Complications experienced during therapy included pulmonary edema, dilutional hyponatremia, aneurysmal rebleeding, coagulopathy, hemothorax, and myocardial infarction. Elevating systemic arterial pressure in states of cerebrovascular insufficiency resulting from vasospasm is safe if meticulous attention is paid to physiological, biochemical, and hematological parameters, with the exception that it may be hazardous in the presence of an untreated ruptured or intact aneurysm. Intravascular volume expansion and induced hypertension are effective in reversing ischemic deficits from vasospasm provided that treatment commences before cerebral infarction and that adequate pressures are maintained for a sufficient period. The production of a hypervolemic state by the use of colloid and crystalloid infusion accompanied by atropine blockade of the vagal depressor response and blunting of the diuresis with vasopressin enables arterial pressure to be elevated for longer than 1 week.