Peptic ulcer of the duodenum and stomach is one of the most common diseases of internal organs. The clinical picture of peptic ulcer is characterized by polymorphism and depends on the localization of the ulcerative defect, its size and depth, the secretory function of the stomach, the age of the patient. The purpose of this study is to determine the size and shape of the ulcerative defect in the duodenum in case of erosive and ulcerative changes in the gastroduodenal mucosa, as well as to study the pH of the environment in the duodenum, which is necessary to optimize the treatment of this pathology, this will prevent the development of complications.