The pharmacological specificity and the regional distribution of the N-methyl-D-aspartate receptor-associated 5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) binding sites in human postmortem brain tissue were determined by binding studies using (+)-[3H]MK-801. Scatchard analysis revealed a high-affinity (KD = 0.9 +/- 0.2 nM, Bmax = 499 +/- 33 fmol/mg of protein) and a low-affinity (KD = 3.6 +/- 0.9 nM, Bmax = 194 +/- 44 fmol/mg of protein) binding site. The high-affinity site showed a different regional distribution of receptor density (cortex greater than hippocampus greater than striatum) compared to the low-affinity binding site (cerebellum greater than brainstem). The rank order pharmacological specificity and stereoselectivity of the high-(cortex) and low-(cerebellar) affinity binding sites were identical. However, all compounds tested showed greater potency at the high-affinity site in cortex. The results indicate that (+)-[3H]MK-801 binding in human postmortem brain tissue shows pharmacological and regional specificity.