The aim was to determine the prevalence of Helicobacter heilmannii-like organisms in human gastric biopsies and the associated histology compared with that of Helicobacter pylori-bearing gastric biopsies. Furthermore, the feasibility of culturing H. heilmannii was examined. A consecutive series of 727 gastric biopsies from 650 patients were prospectively scrutinized for H. heilmannii. Their distribution pattern was recorded as well as the affiliated morphology of the gastric mucosa. Additional biopsies from some of the patients were examined microbiologically. Four cases (0.6%)(95% confidence intervals: 0.01-1.2%) of the examined material harboured H. heilmannii. The bacterial burden was graded as sparse in three cases, moderate in one case. The distribution pattern was patchy; thus, in no case did all biopsies from one endoscopy comprise H. heilmannii. Adhesion to epithelial cells was infrequent. A mild gastritis, active in three cases, characterized all biopsies. Lymphoid aggregates occurred in biopsies from three patients. Micropapillary tufting of the epithelial layer and intestinal metaplasia were not apparent. Culture studies proved successful in the one of the four cases assayed. In conclusion the morphology of H. heilmannii-bearing mucosa deviates from that of H. pylori-associated mucosa by the absence of epithelial damage in the former. This observation can in part be explained by the predominant location of H. heilmannii at a distance from the epithelium in contrast to the conspicuous H. pylori adhesion to epithelial cells, coupled with a usually low bacterial burden and patchy occurrence of H. heilmannii as opposed to the generally more heavy infestation with H. pylori.