In the present study, we examined by immunohistochemistry the formation and distribution of 8-nitroguanine, a sensitive marker of nitrosative DNA damage, in rat stomach of rats subjected to water immersion restraint stress (WIR). WIR induced an increase in 8-nitroguanine content of gastric gland epithelium. 8-Nitroguanine immunoreactivity, which was observed mainly in the nuclei of stomach epithelium, increased with the severity of inflammation. Expression of iNOS was also observed in the inflammatory cells of lamina propria. Therefore, it is logical that iNOS-mediated nitrosative stress must participate in the development of ulcers through apoptotic cell death linked to the formation of 8-nitroguanine during chronic inflammation. Taurine administration attenuated stress-induced gastric mucosal injury. These results demonstrate that nitrosative stress participates in stress-mediated ulcer formation. Taurine exerts a prophylactic effect against mucosal lesions of the stomach caused by stress. This effect of taurine may have a potential clinical benefit in preventing gastritis associated with stress.