Nitric oxide(NO) relaxes vascular and non-vascular smooth muscles. Furthermore, recent studies have implicated that NO acts as an important neurotransmitter in autonomic innervation, and may mediate inhibitory nonadrenergic-noncholinergic(I-NANC) effect in the airway. Attempts to localize NO acting as a neurotransmitter have been hampered by its short life-time and gaseous nature. But NO can be localized indirectly by the histochemical staining of nicotinamide adenine inucleotide phosphate(NADPH)-diaphorase, because it is demonstrated recently that NADPH-diaphorase is identical to NO synthase, the enzyme responsible for synthesis of NO. The aim of this study is to localize the distribution of NADPH-diaphorase positive nerves in the rat nasal mucosa by histochemical staining for NADPH-diaphorase, and to determine its origin by utilizing retrograde tracing with fluorogold(FG). In conclusion, NADPH-diaphorase positive nerves distribute around blood vessels, submocosal glands, and in the subepithelial layer of the nasal mucosa and their origin is the pterygopalatine ganglion. These findings imply that NO may be colocalized to the nasal mucosa.