Objectives: To investigate the change of vitamin C concentration (ascorbic and dehydroascorbic acid) in gastric juice after anti-Helicobacter pylori treatment, and to relate any observed change to gastric pH, inflammatory compromise of the gastric mucosa, plasma vitamin C concentration, and smoking habits. Methods: Plasma and gastric juice vitamin C, fasting gastric juice pH, gastric histology, and smoking status were studied in 70 patients with H. pylori-associated gastritis before and after therapy. Results: Gastric juice ascorbic acid increased significantly after H. pylori clearance. For the most part, this change was confined to patients who experienced reduction of gastric pH. It was also related to improvement of the compromise of the gastric epithelium, reduction of the proportion of vitamin C composed by dehydroascorbic acid, and increase of the gastric juice/plasma vitamin C concentration gradient. Smokers had lower vitamin C concentrations in plasma and gastric juice before and after H. pylori clearance than nonsmokers. Conclusions: The findings are consistent with a causal association between H, pylori infection and low ascorbic acid levels in gastric juice, and support two mechanisms for this association: increased oxidation and a decreased secretion of ascorbic acid.