The regional cerebral blood flow of 27 young (mean age 24 years) schizophrenic patients was measured using the intravenous 133Xe method. The results were compared with those obtained from a group of age- and sex-matched control subjects. The main findings of the study were as follows: (a) the gray matter mean values of cerebral blood flow for both hemispheres were slightly but significantly lower in the schizophrenic group, and the statistical variance was significantly greater in the patients than in the control group; (b) the mean value for each hemisphere was found to be significantly lower for the right hemisphere; (c) the physiological hyperfrontal patterns of cerebral blood flow were identical in patients and controls; (d) visual hallucinations were associated with a reduction of regional cerebral blood flow in the temporo-occipital regions; and (e) antipsychotic medication did not appear to influence gray matter cerebral blood flow.