The effects of the neuropeptide molecules, adrenocorticotrophic hormone or alpha-melanocyte stimulating hormone, on various parameters of in vitro nerve growth, have been studied in the presence and absence of a small applied electric field. Striking effects on rates of nerve growth occurred. Selected concentrations of either substance alone, produced a three- to fourfold increase in nerve growth rate; other concentrations were inhibitory. The applied electric field alone increased rates of growth threefold. Further augmented rates of growth were seen when either neuropeptide was present simultaneously with an applied field. Under these latter conditions, galvanotropic (cathodal) orientation persisted, while nerve branching was suppressed. Given the clinical interest in melanocortin-stimulated nerve regeneration, perhaps a combined electrical and neuropeptide approach would be warranted.