Campylobacter pyloridis has been associated with acid-peptic disease in centres outside Canada. The authors conducted a pilot study to see if this association existed in Toronto. Patients in whom esophagogastroscopy was indicated on clinical grounds were arbitrarily selected for determination of the presence of C. pyloridis. Included in the study were 100 patients who underwent 105 endoscopies. In 75 patients (80 endoscopies) there was some form of acid-peptic disease (inflammation or ulceration of stomach or duodenum). Of those with acid-peptic disease, 34% had C. pyloridis compared with 4% among patients without acid-peptic disease (p less than 0.01). Men with acid-peptic disease were more likely to harbour C. pyloridis than women (48% versus 16%, p less than 0.01). The organisms were curved gram-negative rods that appeared as small colonies after 4 days of incubation under microaerobic conditions. They were strongly urease positive. There was considerable heterogeneity of endoscopic diagnoses. Future clinical studies of C. pyloridis need careful endoscopic and histologic classification.