Campylobacter-like organisms (CLOs) were histologically detected in 230 (74.5%) of 310 patients undergoing endoscopy with multiple gastric biopsies for symptoms suggestive of upper digestive disease. CLOs were found in 78.6% of nonulcerous dyspeptic patients, 82.2% of healed ulcers, 88.2% of duodenal or pyloric ulcers and 90.0% of gastric ulcers but only in 46.9% of gastric stumps and 47.6% of nonulcerous patients without dyspepsia. Among 274 subjects with gastritis, CLOs were found in 83.9%, while none of the 36 gastritis-free stomachs harbored CLOs. Severe atrophic gastritis was less frequently infected with CLO (55.5%) as compared with superficial, interstitial or preatrophic gastritis (84.4%). CLOs were only slightly more frequent in the presence of intraepithelial granulocytes and were never found in areas of complete intestinal metaplasia. Foveolar and superficial epithelia heavily infected with CLOs showed peculiar ultrastructural changes (micropapillary hyperplasia with luminal bulging of mucous cells, cytoplasmic vacuolization and edema, etc.) suggesting a direct link between CLO infection and epithelial damage, which in turn may have a role in the genesis of mucosal inflammation.