We examined the regulation by nerve growth factor (NGF) of the immediate-early gene (proto-oncogene) c-jun in adult dorsal root ganglion (DRG) neurons using immunocytochemistry to c-JUN (the protein product of the proto-oncogene c-jun). Following a sciatic nerve crush, the injury-induced increase in c-JUN-like immunostaining was reduced in DRG neurons by continuous intrathecal infusion of NGF for one week. Conversely, in intact DRG neurons (i.e., without Wallerian degeneration), c-JUN-like immunoreactivity was markedly increased following four weeks of daily NGF antiserum injections (to remove target tissue-derived NGF) into the hindfoot. Taken together, these findings indicate that nerve transection (axotomy) results in a loss of target tissue-derived NGF leading to induction of the transcription factor c-jun which may play a role in axonal regeneration.