<正> Objective: To study the relationship between nitric oxide synthase （ NOS） expression in human gastric mu-cosa and Helicobacter pylori （H. pylori） infection. Methods: Gastric mucosa samples were obtained from antrum of 33 patients received gastroendoscopy. H. pylori infection was confirmed by Giems staining and bacteria culture under mi-croaerophilic conditions. Expression of iNOS

eNOS and nitrotyrosine were detected by immunohistochemistry. Results: （1） The positive rate of H. pylori infection was 66. 7% （22/33） . （2） iNOS positive staining in inflammatory cells was detected in 77. 3% （17/22） of samples with H. pylori and 27. 3% （3/11） without H. pylori infection （P < 0.01）. （3） eNOS expression in inflammatory cells was found in 77. 3% （17/22） of samples with H. pylori and 18.2% （2/11） without H. pylori infection （ P < 0. 01） . （4） Nitrotyrosine expression in inflammatory cells was observed in 59. 1% （ 13/22） of samples with H. pylori and 54.5%（6/11） without H. pylori infection （P>0.05）. （5） Moderate a