Cerebral blood flow measurements with single photon emission tomography and 133Xe inhalation was performed in 18 patients with hematomas, 14 thalamo-capsular, 4 capsulo-lenticular. In thalamo-capsular cases and in standard conditions, ipsilateral hemispheric C.B.F. and contralateral cerebellar C.B.F. were decreased; a concomitant depression of frontal and temporal C.B.F. was often noted. A similar change was found in capsulo-lenticular cases, the frontal C.B.F. being however less depressed. An attenuation of interhemispheric asymmetry was often found after acetazolamide intravenous injection. A significant correlation was demonstrated between interhemispheric asymmetry index (AI) and frontal and temporal AI.