With the aid of [3H]thymidine autoradiography it was established that in the developing cerebellum of the rat the Bergmann glia cells come into existence essentially during days 9, 10, 11 and 12 of the postnatal life. In the context of this finding migratory cells arising out of the external granular layer were evaluated before the origin of the Bergmann glia cells and during the period of their genesis, in order to determine the nature of cues that they followed in their path of migration. The migratory cells were observed in close association with the dendrites of the Purkinje cells, growth cones related to the dendritic branchings of the Purkinje cells, the somata of Purkinje cells, other migratory cells, and thin-caliber gray-looking fibers of unknown origin. On the basis of these findings and also those reported by Rakić26 it was concluded that any available surface providing contact guidance could serve the migratory cells in defininf their path of migration. The issue pertaining to the locomotive force required for migration of the cell has been briefly considered.