Growth/differentiation factor 5 (GDF5) is a member of the transforming growth factor-beta (TGF-beta) superfamily that has potent neurotrophic and protective effects on dopaminergic neurones and is expressed in the developing rat substantia nigra (the ventral mesencephalon; VM). GDF5 has the potential to be used in the treatment of Parkinson's disease (PD), a neurodegenerative disorder characterised by the selective degeneration of nigrostriatal dopaminergic neurones. One therapy being explored for PD involves transplantation of fetal VM tissue into the striatum in order to replace lost dopaminergic neurones. The majority of transplantation studies have used transplants incorporating the whole VM. The principal location of dopaminergic neurones in the E14 rat VM is in the medial VM. In the present study, the effects of GDF5 on cultures prepared from medial, lateral and whole E14 rat VM tissue were compared. GDF5 treatment increased the number of dopaminergic neurones in whole and lateral, but not in medial, VM cultures, whereas it increased total cell number in medial, but not in whole or lateral, VM cultures. RT-PCR studies showed that the receptors for GDF5 were differentially expressed in E14 VM; the expression of BMPR-IB and Ror2 was low in medial but high in lateral VM tissue. This study suggests that GDF5 increases the number of dopaminergic neurones in whole VM cultures by acting on BMPR-IB and Ror2-expressing cells in the lateral VM.