A number of neurotrophic factors have been implicated in the prenatal development of the enteric nervous system. Although several of these factors continue to be expressed in the gut during postnatal life, their actions on postnatal enteric neurons are not understood. One such factor is the neurotrophin, NT-3. Both NT-3 and its high affinity receptor, trk C, are expressed in the postnatal gut at a time when changes in the density of intestinal innervation are occurring. We have therefore examined the effects of NT-3 on postnatal myenteric neurons, using dissociated cell cultures of ganglia isolated from 6-8 day postnatal rat small intestine. Effects of NT-3 on neurite outgrowth and neuronal and glial cell numbers were measured after 2 days in vitro. The proportion of neurons was increased in NT-3 treated cultures, as was the proportion of neurons that extended processes. NT-3 treatment, at concentrations of between 0.1 ng and 10 ng/ml, also resulted in a significant increase in mean total neurite length. These results indicate that NT-3 may play a role in the postnatal development of the enteric nervous system.