The development and regeneration of rat dopaminergic neurons of the ventral mesencephalon was studied in organotypic slice cultures. Single ventral mesencephalon cultures and co-cultures of ventral mesencephalon with striatum (a target region) or cerebellum (a non-target region) were prepared from postnatal day 1 Wistar rats. Cultures were processed for tyrosine hydroxylase and glial fibrillary acidic protein immunoreactivity, at two day intervals, for an overall incubation period of 20 days. Analysis of these cultures revealed that the striatal target tissue, exerted neither a trophic nor a tropic influence on the tyrosine hydroxylase immunoreactive neurons. In both single and co-cultures, tyrosine hydroxylase immunoreactive neurites projected radially from the ventral mesencephalon slice. However, in striatal co-cultures, tyrosine hydroxylase immunoreactive neurites were seen penetrating the striatal slice, whereas in cerebellar co-cultures no tyrosine hydroxylase immunoreactive neurites entered the cerebellar tissue. Glial fibrillary acidic protein positive cells actively migrated from the tissue sections, however tyrosine hydroxylase immunoreactive neurite outgrowth was not guided by these glial cells. Tyrosine hydroxylase immunoreactive neurites terminated once they had penetrated the striatal slice. This retardation of neurite growth by a target region could be important in establishing and reinforcing synaptic connections in the developing nigro-striatal pathway.