Ranitidine is an H2-receptor antagonist that was released recently for use in the treatment of acute duodenal ulcer disease, Zollinger-Ellison syndrome, and systemic mastocytosis with gastric hypersecretion. The pharmacokinetics, efficacy, adverse effects, and clinical utility of ranitidine are presented. The drug is similar in therapeutic effect to its predecessor, cimetidine, yet has certain advantages over cimetidine in clinical applications.