The shape of a neurone--the projection and branching pattern of axons and dendrites--appears to be determined by a combination of intrinisic and environmental influences. We have previously shown that striatal target neurones influence the biochemical maturation of ascending mesencephalic dopamine (DA) cells in culture, as well as the elongation rate of DA neurites. Using a similar approach in which the morphology of individual DA cells can be studied after 3H-DA uptake and autoradiography, we now report on in vitro neurone-glia interactions and show that glial cells exert a morphogenetic effect on DA neurones. Dopaminergic neurones from the mesencephalon were plated on glial monolayers prepared either from the striatal or the mesencephalic region of the embryonic brain. On mesencephalic glial cells the majority of DA neurones develop a great number of highly branched and varicose neurites, whereas on striatal glia they only exhibit one long, thin and rather linear neurite. These results demonstrate that glial cells from two different brain regions have distinct properties which could be used to define neuronal polarity observed in vivo.