The aim of the study was to study the morphological features of the inflammatory processes of the mucous membrane of various parts of the stomach and duodenum in patients with chronic gastritis and duodenitis. 24 patients (18 men and 6 women) were observed with chronic gastritis and duodenitis associated with Helicobacter pylori. The average age of the patients was 47 years. 120 biopsy samples of the mucosa of different parts of the stomach and duodenum were studied using histological, histochemical, morphometric and microbiological methods. Histological and microbiological examination of biopsy specimens revealed chronic antral gastritis, chronic fundal gastritis and chronic diffuse pangastritis. Superficial chronic duodenitis was rare and was erosive only in 11.4%. Helicobacter pylori in biopsy of stomach samples were detected more often in associations of various forms. Chronic antral gastritis of the type B was characterized by a predominantly high activity of the pathological process, moderate atrophy of the pyloric glands and a high incidence of small bowel metaplasia. Violations of the microvasculature, hemorrhages in the interfoveolaris part, plethora of blood vessels, and sludge in the capillaries were revealed in the lamina propria of the mucosa of the antrum of the stomach; lymph nodes with pronounced germinal centers were observed in half the cases. In the interfoveolaris part of the lamina propria of the mucous membrane, a high density of inflammatory cell infiltrate was observed, in which plasmocytes, lymphocytes, fibroblasts, fibrocytes, eosinophilic and neutrophilic granulocytes, macrophages were detected. Chronic fundal gastritis of the type B was characterized mainly with moderate and minimal activity of the pathological process. Helicobacter pylori were detected on the surface of the entire epithelium. Focal small intestinal metaplasia and atrophy of the main glands were rarely detected. Atrophy of the main glands was predominantly and minimal and was often combined with hyperplasia of parietal cells. The density of the inflammatory cellular infiltrate remained high; plasmocytes, lymphocytes, fibroblasts, eosinophilic and neutrophilic granulocytes, macrophages were found in it (in decreasing order). The study of biopsy samples of the mucosa of different parts of the stomach and duodenum against the background of contamination with a pyloric helicobacter revealed the presence of chronic antral, fundal gastritis and chronic duodenitis of the II-III degree with the development of small bowel metaplasia and dysplasia.