The therapeutie efficacy of ranitidine was evaluated itn 48 in- and out- patients with endoscopically diagnosed 18 cases of gaetric ulcer and 30 casea of ducnienal ulcer. In the open study, every pabenta was treated with ranitidine 150 mg b.i.d. for 4 weeks, and waa followed up by gastroscopy after 4 weeks of the treatment. The reeults obtained were summarized as follows; 1) 15 out of 18 cases (83. 3%) of gastric ulcers and 26 out of 30 cases (86. 7%) of duodenal ulcers had been completely healed up in 4 weeks. 2) There was a significant relationship between healing of ulcer and the relief of symptoms (x =6.12, P<0.005).3) There were no significant untoward reactions, efther subjective or objective, to the administration of the drug, except one case of severe epigastic discomfort. In conclusion ranitidine appears to be fairy effective and safe for the treatment of patient with peptic ulcr diseases.