Background/aims: Much is known about the gastric tissue damage that is associated with hypovolemic stress, but gastrointestinal bleeding due to gastric injury and further gastric injury due to hypovolemia have not been evaluated in previous research. The aim of this study was to assess oxidative gastric tissue damage specifically linked to hypovolemia in patients with upper gastrointestinal bleeding. Methods: The study included 30 patients who presented with acute upper gastrointestinal bleeding and 30 controls. Each patient's history and laboratory findings were recorded, and multiple biopsies of the gastric antrum were obtained at diagnostic endoscopy on admission (day 1) and five days later. A set of antral biopsies was also collected from each control subject. Each tissue specimen was analyzed for levels of glutathione peroxidase, superoxide dismutase and catalase activity, and level of malondialdehyde. Results: First day glutathione peroxidase, superoxide dismutase and catalase levels were significantly lower and malondialdehyde levels were higher than on the 5(th) day, and 1(st) day and 5(th) day levels were significantly different from controls (p<0.05). A moderate level of correlation was detected between catalase and hemoglobin (r:-0.59) and hematocrit (r:-0.61) and between malondialdehyde and systolic blood pressure (p:0.58), hematocrit (r:0.45) and hemoglobin (r:0.49). Conclusions: In this study, gastric tissue oxidative markers showed antral oxidative changes to be significantly correlated with patients' hemodynamics. Oxidative stress may not be a clinical condition but it obviously shows gastric tissue damage and may explain many of the patients' additional diagnosis of gastric erosions. Interestingly, the oxidative change does not completely recover even on the 5(th) day.