We have investigated the radioligand binding properties of D1 and D2 dopamine receptors in postmortem brains from schizophrenic patients. Consistent with previous reports, the schizophrenic population demonstrated a significant 56% increase in D2 dopamine receptor density. Importantly, the D1 dopamine receptor density was significantly reduced by 43%. These alterations in dopamine receptor densities resulted in a highly significant difference in the ratio of D2/D1 dopamine receptors between schizophrenic patients and controls. A correlation between D1 dopamine receptor density and age was apparent in the schizophrenic patients: D1 dopamine receptor density decreased markedly with age and the linear regressions of D1 dopamine receptor density versus age in both the controls and schizophrenic patients had similar slopes. These results may have clinical implications for the treatment of schizophrenia and tardive dyskinesia.