Attention has been recently adverted to the Helicobacter pylori (H. pylori) by the fact, that its association with occurrence of gastroduodenal ulcer and gastric carcinoma had been justified. Our current understanding about metabolism and physiology of it is still not full, however, great strides have been made as for the methods of investigation during the last 16 years. Complete genome sequence of pathogenic strain of the bacteria have recently became identified, by which certain fundamental aspects of biology of H. pylori have been highlighted. Based on data, infection may presumably act as a cofactor to the development of peptic ulcer disease and carcinogenesis, however, details of pathomechanism are still unclear. Variability and genotype of bacteria, immune reactions and genetic patterns of host organism and mechanisms sustaining the balance of mucosal integrity may have additional influence. This study provides an overview on the current understanding about molecular biology of H. pylori.