GDNF is a disulfide-bonded homodimeric glycosylated protein of 134 amino acids. The amino acid sequences inferred from rat and human cDNAs are 93% identical. The proteins contain seven conserved cysteine residues in the same relative spacing found in all members of the TGF-beta superfamily of proteins. In embryonic midbrain cultures GDNF promotes the survival and morphological differentiation of dopaminergic neurons and increases their high-affinity dopamine uptake.