The zonal organization of the corticonuclear and the olivocerebellar climbing fiber projections to the vermis of the cerebellum of the rat was compared to the pattern of zebrin-positive and zebrin-negative bands in material double-stained for zebrin II and for different anterograde tracers injected in subnuclei of the inferior olive, or retrograde tracers injected in the cerebellar and vestibular target nuclei of the Purkinje cells of the vermis. Projection zones A(1), A(X), X, B, C(X) in the vermis and A(2) (accessory A zone) and C(2) in the hemisphere were defined by their efferent corticonuclear and their afferent climbing fiber connections, and were found to share the same topographical framework with the zebrin pattern.