Cerebral blood flow (CBF) was measured in 90 patients who underwent early aneurysmal clipping after subarachnoid hemorrhage (SAH). Measurements were made by a noninvasive, two-dimensional method involving intravenous injection of 133Xe. Patients of Hunt and Hess grades I and II exhibited normal to slightly subnormal CBF, without significant changes, during the study period. Grades III-V patients had almost normal CBF in the early postoperative period, but their CBF gradually decreased, becoming significantly low after day 31. It is noteworthy that in grades IV and V patients, CBF was abnormally high in the acute stage, relative to their poor neurological condition; these patients were considered to have the "global luxury perfusion syndrome." The syndrome was not uncommon in patients with severe SAH. Possible causative or contributory factors are attempts to surgically reduce intracranial pressure, which leads to increased cerebral perfusion pressure, and concomitant global dysautoregulation. In patients with this syndrome, maneuvers intended to increase CBF should be avoided, as they may aggravate brain swelling or cause hemorrhagic events. Positron emission tomographic studies will provide more accurate and useful information concerning the management of SAH patients.