Although the presence of gastric bacteria has been long established, the recognition and isolation of Campylobacter pylori and similar organisms has opened a new era in the understanding of inflammatory gastroduodenal conditions. Visualization or isolation of gastric Campylobacter-like organisms (GCLOs) is significantly associated with histologic evidence of gastritis, especially of the antrum. Correlation with peptic ulceration also exists but probably is due to concurrent antral gastritis. Outbreaks of hypochlorhydria with concomitant gastritis have been attributed to GCLO infection, and a human volunteer became ill after ingesting C. pylori. Despite rapid microbiologic characterization of the organisms and the epidemiology, pathology, and serology of infection, the pathogenetic significance of GCLOs remains unknown. Whether GCLOs cause, colonize, or worsen gastritis must be considered an unanswered question at present. The efficacy of antimicrobial treatment of GCLO infection on the natural history of gastritis is not presently resolved. Nevertheless, GCLOs are at the least an important marker of inflammatory gastroduodenal disease, and attempts to ascertain their clinical significance are clearly warranted.