The extent of the olivocerebellar projection was examined in the rat using autoradiographic techniques. In animals in which [3H] leucine encompassed the whole olive unilaterally (4 cases), the vast majority of olive cells was densely labelled and climbing fibers were heavily labelled throughout the contralateral hemicerebellum...all regions of the cerebellar cortex receive afferent from the inferior olive which terminate as climbing fibers.