We have investigated the anatomic localization of dopamine D1 and D2 receptors in the human brain using selective high affinity ligands for both types of dopamine receptors and the technique of receptor autoradiography. Dopamine D1 receptors were labeled in postmortem human brain tissue sections using the antagonist [3H]SCH 23390. Dopamine D2 receptors were labeled in consecutive tissue sections using the agonist [3H]205-502 and the antagonist [3H]spiroperidol. D1 and D2 dopamine receptors presented a heterogeneous distribution in the human brain. The highest concentrations of both D1 and D2 receptors were found in parts of the basal ganglia, particularly the nucleus caudatus and putamen. Lower concentrations were seen in other areas for example, the lateral globus pallidus was enriched in D2 receptors and the medial globus pallidus in D1 receptors. The substantia nigra contained intermediate densities of both D1 and D2, D1 receptors being present in higher concentrations. Dopamine D1 receptors were also localized in areas outside of the basal ganglia, particularly in the neocortex, amygdala and hippocampal formation. Dopamine D2 receptors were also present in areas outside of the basal ganglia, the most significant densities being found in the hippocampal formation. We observed a marked age-dependent decline in the density of D1 receptors during the first decades of life. In contrast, D2 receptor concentrations appeared to be unaltered with age. The distribution and densities of dopamine receptors were examined in 12 cases of Parkinson's disease and compared to a control adult population. No significant differences in density and distribution were seen for either D1 nor D2 receptors.