Using quantitative autoradiography, we examined the ability of NBQX (2,3-dihydro-6-nitro-7-sulfamoyl-benzo(f)-quinoxaline), S-AMPA (alpha-amino-3-hydroxy-5-methylisoxazole propionic acid), L-glutamate and NS-257 (1,2,3,6,7,8-hexahydro-3-(hydroxyimino)- N,N,7-trimethyl-2-oxobenzo[2,1-b:3,4-c']dipyrrole-5-sulfonam ide) to compete for [3H]AMPA binding sites in several forebrain regions and cerebellar cortex. NBQX had a higher affinity (P < 0.0001) in cerebellar molecular layer than in any forebrain region, whereas the opposite was true for AMPA (P < 0.001). L-Glutamate and NS-257 had different regional patterns of displacement. Consequently, cerebellum and forebrain have distinct rank orders of potency for AMPA receptor ligands. These results suggest that there are regional variations in the pharmacological specificity of AMPA receptors.