Qualitative and quantitative in vivo studies were performed on the development of the neuropeptide vasoactive intestinal polypeptide (VIP) in the peripheral nervous system of quail embryos. VIP-like immunoreactivity (VIPLI) was found by radioimmunoassay (RIA) from the sixth day of embryonic life onward in the sympathetic chain, the esophagus and duodenum, and from day 15 of incubation onward in the adrenal glands and the nodose ganglia. By using immunocytochemistry, we identified cells expressing VIPLI in sensory spinal ganglia of 13- to 15-day-old embryos. In neural crest cultures, cells expressing the VIP phenotype differentiated constantly under various culture conditions, in contrast to other phenotypes which had specific medium requirements, i.e. adrenergic cells or substance P-containing neurons.