Abstract The present study has investigated whether nitric oxide (NO) is involved in neurotransmission of rat vagal afferent neurons. The diethylamine-NO complex (diethylamine-NO, 10–100 μM) and S-nitroso- N-acetylpenicillamine (3–100 μM) both elicited a concentration-dependent depolarisation of the isolated rat nodose ganglion preparation. Pre-treatment with 1 H-[1,2,4]oxadiazolo[4,3- a]quinoxalin-1-one (ODQ, 300 nM), 6-(phenylamino)-5,8-quinolinedione (LY83,583, 30 μM) and Methylene blue (100 μM) all caused a significant shift to the right in the concentration-response curve to diethylamine-NO. Incubation of rat nodose ganglion sections with a 35S-labeled antisense oligonucleotide to neuronal NO synthase resulted in visualisation of the mRNA encoding NO synthase over vagal afferent perikarya. The anatomical findings, therefore, suggest that a number of rat vagal afferent perikarya possess the ability to produce the enzyme required for the biosynthesis of NO. Collectively, these data suggest that NO may be functionally important as a neuromodulator of rat vagal afferent neurons.