Peripheral axotomy of the spinal nerve and avulsion of the ventral roots have been found to induce increase in expression of nitric oxide synthase (NOS) in the spinal motor neurones and the dorsal root ganglion. The present study investigated changes of NOS, using NADPH-diaphorase (NADPH-d) reactivity as the marker, in vagal complex after axotomy in the rat. Eight days after left cervical vagotomy the NADPH-d reactivity was found to be markedly enhanced in the dorsal motor nucleus of the vagus nerve, the ambiguus nucleus, the solitary tract and the nucleus of the tractus solitarius, and the nodose ganglion. This study offers the first evidence of changes in NOS expression in cranial visceral components following axotomy.