The distributions of regional cerebral blood flow (rCBF) and CO2 reactivity were estimated in normal subjects and in patients with ischemic cerebrovascular disorders, using the 133Xe inhalation method. In the normals, hyperfrontal and hyper-fronto-parietal distributions of rCBF and CO2 reactivity were observed. In the patients, the differences in mean rCBF values between anterior and posterior regions decreased in the affected hemisphere. Comparison between the hemispheres revealed that the anterior regions had a decreased mean rCBF value in the affected hemisphere. The CO2 reactivity in the patients was generally decreased in both hemispheres, but not significantly. The originally existing, different distributions of rCBF and CO2 reactivity in normals must be considered in the evaluation of disturbances of vascular reactivity in patients with cerebral disorders.