Recent research suggests that oxidative stress plays an important role in the development of gastroduodenal diseases associated with Helicobacter pylori. We investigated the variation of oxidative stress parameters following administration of antiulcer therapy in 79 patients with duodenal ulcer and chronic gastritis respectively, infected with Helicobacter pylori. Serum and tissue oxidative stress parameters were significantly modified in the period between diagnosis and healing of lesions. The results obtained indicated an increased production of oxygen reactive species at both serum and gastric tissue levels in the patients diagnosed with gastro-duodenal peptic disease. The production was directly correlated with the severity of the injury. In parallel a deficit of the physiological production of endogenous antioxidants was found, also correlated with the severity of the injuries. Antiulcer treatment led to the improvement of the antioxidant status, healing of lesions and eradication of the infection; a significant decrease of the pro-oxidant compounds in the blood and in the tissue was also found, especially at the level of the antral gastric tissue; they were more marked in the patients with duodenal ulcer as compared to those with chronic gastritis