The autoradiographical distribution of [3H]gabapentin, the tritiated analogue of the novel anticonvulsant gabapentin (1-(aminomethyl)cyclohexaneacetic acid) was measured in rat brain. Binding to sections was uniformly inhibited by non-radioactive gabapentin and 3-isobutyl-gamma-aminobutyric acid (3-isobutyl-GABA). Specific gabapentin binding sites were unevenly distributed throughout the brain with the highest level being found in the outer layers of the cerebral cortex (38 +/- 7 fmol/mm2; n = 3) and the lowest amounts in the white matter. In the hippocampus, the distribution of the binding site paralleled the excitatory neuronal input with the highest levels of binding being measured in the outer layers of the dentate gyrus and in the dendritic regions of the CA1 pyramidal cell layer. The binding site appeared absent from the cell body region of granule and pyramidal cells. Lesions performed unilaterally in the striatum using quinolinic acid resulted in a marked loss of [3H]gabapentin binding sites as compared with sham-lesioned animals, suggesting the binding site was localized on neuronal cell bodies. These data complement and extend the results of experiments using [3H]gabapentin with homogenates of rat brain and show the discrete localization of this novel binding site in regions associated with excitatory amino acid input. The data do not support previous indications of an association of the gabapentin binding site and NMDA/glycine receptor complex.