Campylobacter pyloridis is a newly discovered bacterium which has been implicated in gastric pathology. C. pyloridis was looked for by hematoxylin and eosin staining and culture (chocolate and brucella blood agar) in gastric antral biopsies in 136 unselected patients suffering from epigastric pain. The distribution of C. pyloridis positive cases according to the endoscopic diagnosis was as follows: duodenal ulcer (19 positive/21 tested), duodenitis (6/10), gastric ulcer (9/21), gastritis (13/26), and normal endoscopy (21/58). The association was statistically significant for duodenal ulcers (p less than 0.001). All of the 68 C. pyloridis positive patients showed histologic signs of gastritis as compared to 29 of the 68 C. pyloridis negative patients. The two techniques detection were comparable in sensitivity: 57 were detected by culture only and 63 by microscopy only. We also looked for C. pyloridis in biopsies of the body of the stomach in 71 patients. Bacteria were found in 33 of 36 cases with C. pyloridis positive antral biopsies (15 had histologic lesions) but only in 2 of 35 C. pyloridis antrum negative cases. Therefore, C. pyloridis was tightly associated with histologic signs of antral gastritis and with duodenal ulcers when diagnosed by endoscopy.