A multicenter, double-blind, randomized, controlled study was conducted in 234 duodenal ulcer patients to compare the efficacy and safety of the H2-receptor antagonists famotidine and ranitidine in the treatment of duodenal ulcer. Patients received 40 mg famotidine (119 patients) or 300 mg ranitidine (115 patients) once daily at bedtime for 4 weeks. If ulcer lesions persisted, treatment was extended to 6 weeks. Efficacy was assessed by relief of symptoms and endoscopic findings of ulcer healing. Safety was determined on the basis of reports of side effects, results of laboratory tests, and, in selected patients, changes in plasma levels of hormones. The 4- and 6-week healing rates achieved with famotidine were 76% and 91%, respectively, and with ranitidine they were 76% and 87%, respectively; the differences in healing rates for the two drugs were not statistically significant. Similarly, both drugs provided satisfactory relief of pain and dyspeptic symptoms. However, famotidine produced significantly (P less than 0.05) greater relief of postprandial fullness and heartburn. The incidence of untoward effects was low in both treatment groups, and abnormal results in laboratory tests were observed in only one patient, a chronic alcoholic receiving famotidine, who withdrew from the study because of a slight elevation in serum transaminase levels. One patient in the ranitidine treatment group dropped out of the study because of a generalized urticarial rash; however, a causal relationship between drug and effect could not be established. The authors conclude that famotidine may be regarded as the best alternative to ranitidine in the treatment of duodenal ulcer.