The authors analyzed a group of 164 subjects where they collected during gastroduodenoscopy specimens of the gastric mucosa for histological and microbiological examination. Campylobacter pylori (CP) was detected in 37 of 41 subjects with gastritis type B (90.2%), in 36 of 45 patients with duodenal ulcers (80%) and in 15 of 24 patients with gastric ulcers (62.5%) and in one of 15 subjects with gastritis type A. In 8 patients with drug induced and reflux changes the presence of CP was not detected. In the control group of 31 subjects CP was found in 4 (13%). Gastritis type B was diagnosed in 91% of the patients with gastric ulcers and in 93% of patients with duodenal ulcers. Elimination of CP by amoxicillin was successful in 71% of the patients with duodenal ulcers, 67.5% patients with gastric ulcers and in 45% of subjects with gastritis type B. After elimination of CP in all subjects rapid regression or complete disappearance of inflammatory changes was recorded. Within 12 months after elimination of CP and healing of that ulcer a relapse was recorded in 20% of the patients. Based on their observations the authors conclude that CP appears to be the causal factor of gastritis type B and one of the causal factors of peptic ulcers. Elimination of CP improves the course of both diseases.