Extensive studies in the chicken embryo have recently supplied more insights into the development of the enteric nervous system, which mainly derives from the vagal neural crest (i.e., the neural crest opposite somites 1 to 7). Crest cells migrate from this region to and via the developing gut. By means of a double labeling technique of both neural crest cells and cells in the S-phase of the cell cycle, we found that these migrating crest cells still proliferate in the gut. Some cells even go through cell division after the formation of a nerve plexus. Some implications for the pathogenesis of congenital innervation abnormalities such as hyperganglionosis and the aganglionosis of Hirschsprung's disease are discussed.