To determine the mechanisms of gastric mucosal injury associated with Helicobacter pylori infection, we investigated the contents of cytokines and inflammatory cell infiltration in the gastric mucosa. Ninety-six patients with dyspepsia were studied (58 gastric ulcer, 38 nonulcer dyspepsia). Of the 96 patients, 63 were infected with H. pylori as determined by microscopic examination with HE staining, culture of H. pylori, or the rapid urease test. Endoscopic biopsy specimens were obtained from both the antrum and the body to examine interleukin (IL)-8, IL-6, IL-1 beta, and tumor necrosis factor-alpha contents in the gastric mucosa by enzyme-linked immunosorbent assay. Inflammatory cell infiltration was assessed according to the Sydney system. IL-8 content was enhanced in both the antral and body mucosa of the H. pylori-positive patients compared with the H. pylori-negative patients. Furthermore, IL-8 content correlated well with the infiltration of both mononuclear cells and polymorphonuclear cells. These results suggest that IL-8 plays important roles in the pathogenesis of gastric mucosal injury associated with H. pylori infection.