This study aimed at comparing the binding characteristics of [H-3]ketanserin, a high-affinity serotonin 2A (5-HT2A) receptor antagonist, in the prefrontal cortex, hippocampus and striatum of human brain post-mortem. The results indicated the presence of a single population of binding sites in all the regions investigated, with no statistical difference in maximum binding capacity (B-max) or dissociation constant (K-d) values. The pharmacological profile of [H-3]ketanserin binding was consistent with the labeling of the 5-HT2A receptor, since it revealed a competing drug potency ranking of ketanserin = spiperone > clozapine = haloperidol > methysergide > mesulergine > 5-HT. In conclusion, the 5-HT2A receptor, as labeled by [H-3]ketanserin, would seem to consist of a homogenous population of binding sites and to be equally distributed in human prefronto-cortical, limbic and extrapyramidal structures.