With a multidetector scintillation camera regional cerebral blood flow (rCBF) was evaluated in 13 patients with subarachnoid hemorrhage. Mean CBF was subnormal, and there seemed to be a relationship between CBF and severity of the neurological deficit. The regional pattern showed ischemic and hyperemic areas. Vasospasms mostly produced ischemic areas, roughly corresponding to the region supplied by the involved artery. The hyerpemic areas were striking. This hyperemia can perhaps be regarded as a reaction to initial ischemia.