A strong positive correlation has been demonstrated between the (antral mucosal) presence of Campylobacter pylori and active duodenal and gastric ulceration. Moreover, both duodenal and gastric ulcers heal, and remain in remission, as a consequence of therapeutic measures which eradicate C. pylori. However, the Henle-Koch postulates have not been fulfilled, because C. pylori has not been shown to produce ulcers. As for the claim that ulcer disease represents an infection with C. pylori because therapeutic eradication heals ulcers, it has been shown that antibiotics and metronidazole, as well as bismuth subcitrate, exert antiulcer actions by mechanisms which do not involve their antibacterial effects. The association between C. pylori and ulcer disease, which was noted half a century ago, remains unexplained now as it did then.