The peptide toxin omega-conotoxin GVIA (omega-CgTx) has been shown to be a high affinity ligand for N-type calcium channels in the brain. The authors employed [125I]omega-CgTx to localize N-type channels in human hippocampus and cerebellum using autoradiography. Ten micron thick slide-mounted tissue sections of human cerebellum and hippocampus were labeled with [125I]omega-CgTx under various conditions. Specific binding to human cerebellum was virtually irreversible and saturable. It was displaceable by the N-channel antagonist, omega-conotoxin MVIIA, but not by L- or P-channel ligands. Binding sites were heterogeneously distributed with denser binding in the molecular layer than the granule cell layer of cerebellum and with specific laminar patterns evident in the hippocampus. [125I]omega-CgTx should be a useful tool for the study of N-type calcium channels in human brain tissue.