Putative N-type voltage-sensitive calcium channels were localized autoradiographically in thaw-mounted rat brain slices using [125I]omega-conotoxin GVIA as a ligand. Density of the toxin binding sites were highly heterogeneous throughout the brain. The highest density of the binding sites was observed in the glomerular layer of the olfactory bulb, cerebral cortex, molecular layer of the hippocampus, amygdaloid complex, reticular part of the substantia nigra, molecular layer of the cerebellar cortex, and nucleus of the solitary tract. White matter tract regions such as the internal capsule, corpus callosum, fimbria of the hippocampus, fornix, and fasciculus retroflexus showed an extremely low density.