The aim of the study was to examine dynamics of the content of nitric oxide (NO) in gastric juice in Helicobacter-associated gastroduodenal diseases. METHODS 105 patients were examined: 56 - with chronic non-atrophic (antral) gastritis (CNG) and 49 - duodenal ulcer (DU). 25 healthy individuals were studied as control. RESULTS It was found that NO concentration increases in gastric juice at the exacerbation of CNG and DU. Moreover, in patients with CNG with the elimination of Helicobacter pylori and inflammatory activity in the gastric mucosa, NO levels decrease to control values, and in DU patients in remission phase the level of it is markedly reducing, but remains higher than normal. The NO content changes, depending not only on a phase, but also character of a course of a disease, are observed at patients with Duodenal ulcer. At recurrent course UD index of NO in the gastric juice was significantly higher than in newly diagnosed destructive process in the mucosa. CONCLUSIONS The carried out research show that H. pylori infection stimulates the metabolism of NO in the gastric CO. The Increase in the levels of NO can be regarded as a protective reaction in response to the persistence of HP.