Anti-Zebrin II is an antibody directed against a 36kDa aldolase epitope expressed by Purkinje cells. Two patterns of Zebrin II immunolabeling have been described in the cerebellar corpus. In mammalian cerebella, the anti-Zebrin II labels longitudinal zones of Purkinje cells, whereas in teleosts, all Purkinje cells of the cerebellar corpus are Zebrin II immunopositive. An outgroup analysis is required to determine which of these distribution patterns represents the primitive condition for jawed vertebrates. The sister group of the Osteichthyans (ray-finned fishes, amphibians, and amniotes) is the Chondrichthyans (sharks, skates, and rays). In the present study the distribution of Zebrin II irnmunopositivity was examined in the Atlantic stingray and the Southern stingray. Western-blot analysis demonstrates that the Zebrin II antibody recognizes an antigen of the same molecular weight in stingrays, teleosts, and mammals. In stingrays, anti-Zebrin II immunohistochemistry reveals a staining pattern in which all Purkinje cells are immunopositive, no banding pattern or zonal compartmentation is observed. Purkinje cell axon projections to the cerebellar nucleus and the octaval nuclei are also revealed. Within the octaval nuclei, immunopositive Purkinje cell axon terminals and boutons en passant were found in the anterior, descending, and posterior nuclei. These immunopositive profiles are found throughout these nuclei, but they are most dense in the lateral and ventral portions. Except for the dorsolateralmost portion, the magnocellular nucleus does not appear to receive Purkinje cell inputs. Based on these results it is concluded that the Zebrin II distribution pattern in which all Purkinje cells of the cerebellar corpus are immunopositive is the primitive condition for jawed vertebrates.