The autoradiographic distribution of Ca(2+)-sensitive high- and low-affinity binding sites for the N-type calcium channel ligand, [125I]omega-conotoxin GVIA, has been examined in rat brain. Both classes of sites were rather evenly distributed, exhibiting their highest density in cell body rich layers, such as the pyramidal layer of Ammon's horn and the granular layer of the dentate gyrus. In cerebellum, the granular layer was more densely labelled than the molecular layer at low ligand concentration, and this pattern was reversed at high concentration. The presence of 30 mM Ca2+ in the incubation medium revealed the existence of a third class of sites, insensitive to Ca2+, comparably distributed at both concentrations, and apparently absent from cell body rich layers.