Abstract: The effect of glial cell line-derived neurotrophic factor (GDNF) on the growth of mesencephalic dopaminergic neurons and on their survival following exposure to the neurotoxin 1-methyl-4-phenylpyridinium (MPP+) was examined in vitro. In cultures developing under normal conditions, GDNF at 1 ng/ml optimally improved the survival and stimulated the growth of dopaminergic neurons without affecting glial growth. In cultures treated with MPP+, GDNF could not prevent toxicity to dopaminergic neurons. The uptake of [3H]dopamine and the number of tyrosine hydroxylase-positive neurons were similarly reduced by MPP+ in the presence or absence of GDNF. However, after removal of MPP+, GDNF protected dopaminergic neurons from the continuous cell death and stimulated the regrowth of dopaminergic fibers damaged by MPP+. We conclude that GDNF supports the growth of normally developing dopaminergic neurons and stimulates their survival and recovery after damage. These findings suggest that GDNF could be useful in the development of therapeutic approaches to Parkinson's disease, which is characterized by dopaminergic cell loss.