We found a tightly coiled bacterium, Helicobacter heilmannii that is distinct from Helicobacter pylori in the gastric mucosal biopsy of a 55-year-old man and a 30-year-old woman, both of whom had previous history of intermittent epigastric pain. The organisms were distributed in the antral mucosa, which was endoscopically interpreted as demonstrating chronic gastritis in one case, and being normal in the other. Histologically, the affected mucosa presented a mild chronic gastritis without activity and a moderate chronic gastritis with marker activity, respectively. The bacteria seen on haematoxylin eosin stained slides were strongly Giemsa positive, and were also visualized with Warthin-Starry stain. They were negative with the anti-Helicobacter pylori immunohistochemistry, although a few spots of staining could represent some cross reaction. Electron microscopy revealed fragments of bacterium, with its characteristic spiral shape and length of 4-7 mm in the plane of the section. One of the patient was treated medically and the control examination revealed normal antral mucosa without spiral bacteria. Detection of these organisms may provide a new insight into the pathogenesis of human gastritis.