Unlike Helicobacter felis and other Helicobacter species of animal origin, Helicobacter pylori colonizes the lower gastric mucin layer of the stomach and adheres to human gastric epithelial cells. It is still an open question if H. pylori can interact with specific glycoconjugates in the gastric mucin layer. It is possible that colonization of the oral cavity is a first step of a complex infectious process. Most likely resting or slow growing cells of H. pylori interact with Lewis blood group substances in the gastric mucin layer and on the epithelium. This initial colonization is probably followed by binding to specific cell surface glycoconjugates (glycoproteins and glycolipids such as GM3) and specific sialylated or highly sulphated molecules such as cell surface sulphatides and heparan sulphate. H. pylori may also bind to specific phospholipid molecules such as phosphatidylethanolamine on the gastric cells. The adhesion process of certain strains can stimulate 'close' cell adhesion including pedestal formation similar to the phenomenon typical for a special class of enterovirulent Escherichia coli called attaching effacing E. coli. After gastric cell destruction by ammonia and H. pylori toxins (such as the vacuolating toxin) H. pylori may colonize the extracellular matrix (ECM). This phenomenon seems to include binding of cell surface sialic acid specific haemagglutinin to one ECM component, i.e. laminin. It is also likely that H. pylori may use similar events to penetrate intercellular junctions of gastric epithelial cells. These adhesion-penetration phenomena also involve coating of the microbe with host proteins to escape the host immune system and initiate a chronic lifelong infection process.