Background:Nitric oxide has an important role in the pathophysiology of the gastric mucosa. However, to date, it is not clear if nitric oxide plays a cytoprotective or cytotoxic role in the pathogenesis of mucosal lesion.Methods:We have used the NADPH-diaphorase histochemistry that selectively stains cells containing nitric oxide synthase, the enzyme that catalyzes the production of nitric oxide on the antral gastric mucosa of children with antral gastritis.Results:In the lamina propria of the mucosa, the presence of the enzymatic activity was found in perivascular round cells and nerve fibers. In the epithelium, focal positivity to NADPH-diaphorase was found in superficial cells, mainly located in the extrusive zones. The epithelial cells in the pits and glands were negative, in the mucous layer,Helicobacter pyloriwere also stained by NADPH-diaphorase. A singleH. pylori-infected child who was also examined after eradication of theH. pylorishowed during the control examination absence of microorganisms and reduction of the NADPH-diaphorase-positive cells in the mucosa.Conclusions:Our results demonstrate that, in gastric mucosa, endogenous and exogenous structures express a NADPH-diaphorase activity.