Precursors of the neurons that populate enteric ganglia cannot be recognized morphologically when they first enter the gut; therefore embryonic gut in culture, explanted before neurons appear, develops a myenteric plexus that contains cholinergic and serotonergic neurons. The evidence indicates that the developing gut maintains an immature proliferating pool of neuronal precursors that may tentatively and transiently express a given neuronal phenotype. Catecholaminergic expression is an example of such a transient phenotype. It is possible that sequential changes, occurring as a function of gestational age in the enteric neuronal microenvironment and interacting with this persistent pool of neuronal precursors, are responsible for the generation of enteric neuronal diversity. The sequential appearance of the various types of enteric neuron is consistent with this hypothesis. The persistence of a dividing cell population may also be linked to the generation of the large number of enteric neurons.