Helicobacter pylori is one of the most frequently observed pathogenic bacterium that colonizes the human stomach. Colonization of gastric mucosa is the main etiologic factor of the development of duodenal and gastric ulcer diseases and gastric adenocarcinoma. The spectrum of bacterial proteins, especial- ly CagA antigen, cytotoxin VacA and BabA adhesin, are correlated with higher virulence of H. pylori strains. Differences in activities of cytotoxin VacA and CagA antigen are connected with polymorphisms observed in the genes which coded these proteins. However, the main role in pathogenesis of H. pylori infection might play specific interactions between H. pylori and gastric epithelial cell on the molecular level.