The occurrence of Campylobacter pylori (CP) was studied in 180 patients referred for endoscopy. The bacterium was detected by culture, histology (Warthin-Starry staining) and urease test of antral biopsy samples. Patient groups were formed according to endoscopic diagnoses, clinical symptoms and antral mucosal histology. 50 CP positive patients with chronic antral gastritis were treated by bismuth subsalicylate (2,4 g/day) for 3 weeks. Positivity by culture and/or silver-stained histology proved to be the most reliable way for detecting CP. CP was proved in about 30% in patients with normal gastroduodenum (13/42) or with stump gastritis (4/15), in 75% with endoscopic antral gastritis (51/68) and in 89% with duodenal ulcer (49/55). A close relationship between CP and histological chronic antral gastritis could be demonstrated. No causal link between CP positive chronic active antral gastritis and non-ulcer dyspepsia could be verified. The decrease in histological activity of chronic gastritis and in dyspeptic complaints after bismuth salt therapy was found to be independent of CP elimination. The results of control investigations following a therapy-free interval of 7-10 days speak in favour of CP recolonialisation within a relativelly short period. It can be concluded that, despite the undeniable relationship between CP and chronic antral gastritis and duodenal ulcer, further studies are necessary to clarify the clinical relevance of the CP infection.