The relationship between gastro-oesophageal reflux disease (GERD) and Helicobacter pylori is unclear. Recent data indicate that H. pylori probably exerts a protective effect against GERD. In recent years, the interaction between H. pylori, proton pump inhibitors and GERD has been widely studied. Currently available proton pump inhibitors produce significantly higher intragastric pH in H. pylori-positive patients than in those who are H. pylori negative, and this phenomenon may be clinically relevant. The mechanisms responsible for this difference in efficacy are not fully understood, although there are two major theories. Ammonia, produced by H. pylori, is able to neutralize gastric acid, and thus apparently increase the effect of acid suppressive agents (the 'ammonia theory'). The other theory is that decrease in acid output is due to the development of corpus gastritis during treatment with a proton pump inhibitor (the 'gastritis theory'). Treatment strategies to overcome this lowered sensitivity to acid suppression are to increase the frequency/dose of a proton pump inhibitor or to add an H2-receptor antagonist in the evening-but both have pharmaco-economic implications. An agent that could provide adequate pH control regardless of H. pylori status would be highly beneficial in the treatment of GERD, and may also lower treatment costs.