The first H2-receptor antagonist, cimetidine, has been succeeded by ranitidine, and more recently nizatidine and famotidine. Others will doubtless follow. The pharmacodynamic differences between cimetidine and ranitidine, in terms of potency, are not obviously translated into therapeutic differences. Some studies have shown that the increased potency of standard doses of ranitidine affords an advantage, in terms of ulcer healing and relapse, over cimetidine. The therapeutic effects of these drugs can be predicted from their pharmacodynamic profiles and in the doses recommended differences between the newest agents and ranitidine would not be expected. It is, thus, difficult to define a specific clinical role for the newer drugs on the grounds of efficacy. Their importance may relate to the provision of encouragement for future drug development.