Tightly coiled spiral micro-organisms (Gastrospirillum hominis), distinct from Helicobacter pylori, were found in the gastric mucosa of a 66-year-old man with a 4-month history of intermittent epigastric pain. The organisms were distributed in the antral mucosa, which showed erosive gastritis; histologically, the affected mucosa presented moderate to severe chronic gastritis with focal neutrophil infiltration. After a 2-week administration of cimetidine, his symptoms resolved and the active inflammation was reduced, both endoscopically and histologically, but the organisms still remained. Biopsy specimens taken 4 weeks after treatment with minocycline and cimetidine showed normal gastric mucosa without the spiral organisms. The above clinical course suggests the possible role of Gastrospirillum hominis in the pathogenesis of gastritis.