Studies were performed to examine the relation of dopaminergic cells and radial glia in the developing mesencephalon of the rat at ages E12-E20. Dopaminergic cells were immunolabelled with an antiserum which recognizes tyrosine hydroxylase, and radial glia were immunolabelled with a monoclonal antibody which recognizes vimentin. The vimentin-immunoreactive fibres of radial glia were noted at E12. At E12, and more clearly at later time points, the radial glia extended from the aqueduct to the pial surface, and this pattern persisted throughout the prenatal period. Tyrosine hydroxylase-immunoreactive cells were located along the ventral surface of the mesencephalon at age E13. At age E15, E16, and E18 the tyrosine hydroxylase-immunoreactive cells were present from the aqueduct to the ventral pial surface of the mesencephalon and were aligned along radial glia. Our study suggests that radial glia provide paths for migration of dopaminergic cells in the mantle layer from E15 to E18 of the developing mesencephalon. It also suggests that some dopaminergic cells between E15 and E18 may express tyrosine hydroxylase during their migration through the mantle layer and prior to reaching the location they occupy in the adult brain.