Medical management of peptic ulcer disease continues to evolve with the recent introduction of new H2-receptor antagonists, prostaglandin analogs, and a proton pump inhibitor, and clarification of the relationship between suppression of gastric acidity and ulcer healing. Nizatidine and roxatidine acetate, the new H2 blockers, are safe and effective but do not appear to have new properties of clinical importance. The modes of action of omeprazole and the prostaglandins have been clarified. Omeprazole is a prodrug that is protonated and secured in the secretary canaliculus of the parietal cell where the active derivative covalently binds sulfhydryl groups of H+/K(+)-ATPase, thereby irreversibly and profoundly blocking acid secretion. Prostaglandins bind a receptor on the basolateral membrane of the parietal cell, releasing a protein that inhibits cyclic AMP, the second messenger of histamine-stimulated acid secretion. The ulcer-healing properties of prostaglandins can be attributed largely if not entirely to their inhibition of acid secretion. Antacids, on the other hand, may heal ulcers by effects other than acid neutralization, as the low-dose regimens that heal ulcers only weakly neutralize acid. The way in which sucralfate and colloidal bismuth heal ulcers remains unclear; they may do so through multiple effects including, in the case of bismuth, eradication of C. pylori. H2-receptor antagonists continue as first-line treatment for acute DU and GU and the prevention of recurrence. The antacid and sucralfate regimens are less convenient but safe and effective. Misoprostol has a disadvantageous safety profile relative to available agents but is effective in preventing NSAID-induced gastric ulcers. The efficacy of omeprazole in acid-peptic disease is established but the way in which it should be used is still unclear because of long-term safety concerns.