We investigated an antiinflammatory effect of rebamipide [2-(4-chlorobenzoylamino)-3-[2(1H)-quinolinon-4-yl] propionic acid], a gastroprotective agent, in H. pylori-associated gastritis. Eighty-six patients with H. pylori-positive chronic gastritis were enrolled: 53 were treated with rebamipide (300 mg daily for 12 months) and 33 served as controls. Significant decreases in mononuclear cell infiltration into the antrum and corpus were noted in the rebamipide treatment group (before vs after, 1.42 +/- 0.15 vs 1.02 +/- 0.15; P < 0.01 and 1.60 +/- 0.15 vs 1.21 +/- 0.14; P < 0.05, respectively). Levels of infiltrating neutrophil were also decreased in the antrum (before vs after, 0.98 +/- 0.14 vs 0.70 +/- 0.13; P < 0.05) and were associated with a decrease in iNOS production. Sera from patients treated with rebamipide showed a significant decrease in gastrin (276.3 +/- 58.3 pg/ml vs 173.0 +/- 34.2 pg/ml; P < 0.05), whereas no change was observed in the control group. These suggest that long-term rebamipide treatment improved histologic gastritis and decreased serum gastrin levels in H. pylori-associated gastritis.