BACKGROUND Recent studies have shown that acid-suppressive therapy increases the severity of Helicobacter pylori- associated gastritis in the corpus. OBJECTIVE To evaluate interleukin (IL)-8 production in the gastric corpus mucosa before and during acid-suppressive therapy in H pylori-infected patients. METHODS Ten patients with reflux esophagitis (five H pylori-positive and five H pylori-negative) were treated with omeprazole 20 mg. Serum gastrin concentrations, H pylori colonization density and mucosal IL-8 levels in the corpus were investigated at entry and two weeks after starting therapy. IL-8 levels were measured by ELISA. The organism density was determined, and scored according to area occupied by the bacterial colonies. The presence of H pylori was assessed by rapid urease testing and histological finding of gastric biopsy specimens. RESULTS In H pylori-positive patients, concentrations of IL-8 during therapy significantly exceeded those before therapy (36.2+/-6. 8 versus 18.3+/-3.8 pg/mg protein; P<0.05) without altering H pylori density. In H pylori-negative patients, IL-8 levels were similar before and during therapy (6.1+/-2.7 versus 6.3+/-3.0 pg/mg protein). Concentrations of gastrin during therapy were significantly higher than those before therapy in all patients. CONCLUSIONS The results suggest that acid suppression increases mucosal IL-8 levels in H pylori-infected patients with reflux esophagitis.