The neuropeptide vasoactive intestinal polypeptide (VIP) increases the activity of tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of catecholamines, in cultured chicken sympathetic neurons. We report here that VIP acts by increasing TH mRNA levels in these cells. Induction of TH mRNA is transient and reaches maximal values 6-8 h after the addition of the peptide to the cultures. TH mRNA levels return to control values after 1-2 days. The quail cDNA probe detects a single mRNA species of approximately 9 kb in RNA extracted both from embryonic chicken sympathetic neurons and adult quail adrenal medulla.