In mammalian cerebella the distribution of high affinity GABA A and benzodiazepine binding sites does not parallel each other. Differences in the molecular structure of the receptor complex or conformational changes have been proposed to explain the lack of a colocalization of these binding sites. Using radio- and immunohistochemistry we were able to obtain similar results for cerebella of non-mammalian species, indicating that the respective distribution of the binding sites is well conserved throughout vertebrate evolution. The γ-aminobutyric acid agonist [ 3H]muscimol and the β-subunit specific antibody bd-17 strongly labeled the granular layer. The radioligands for the benzodiazepine binding site [ 3H]flunitrazepam and [ 3H]Ro 15–1788 revealed species variation in the ratio of benzodiazepin receptor density in the granular and molecular layers. In human and pig cerebellum, the localization of antigenic sites recognized by the α-subunit specific antibody bd-24 deviates from the distribution of the benzodiazepine binding sites.