The aim of the study was to compare the effectiveness of ranitidine and cimetidine in accelerating the healing of chronic gastric ulcer. 44 outpatients with endoscopically proven gastric ulcer whose duration of symptoms was greater than 4 weeks and who were without major systemic disease were studied. Patients were randomly allocated to receive either ranitidine, 150 mg twice a day or cimetidine, 200 mg three times a day and 400 mg at night for 4 weeks. If the ulcer had not healed, treatment was continued for a further 4 weeks, when patient assessment and endoscopy were repeated. By 4 weeks, 13 of 22 patients taking ranitidine (59%) and 14 of 22 patients taking cimetidine (64%) had healed (p2 = 1.0, 95% confidence interval - 20%, 38%). At 8 weeks, 91% on ranitidine and 91% on cimetidine had healed (p2 = 1.0, 95% confidence interval - 18%, 18%). Symptomatic improvement was similar with both drugs. Smoking did not influence healing rates. There were no major side effects with either medication. It is concluded that ranitidine and cimetidine are of similar efficacy in accelerating the healing of chronic gastric ulcer.