Since the recognition and first culture of Campylobacter pylori (Cp) the hypothesis of a pathogenic role has been strengthened by numerous investigations. Its close association with active chronic gastritis and even active duodenitis, and the disappearance of these pathologic conditions with antimicrobial treatment suggest a pathogenic role for Cp in active chronic gastritis. The close association of antral gastritis with duodenal ulcer (DU) suggests that Cp associated active chronic gastritis may be an important precondition for the development of DU. Therapy studies so far using either bismuth, antibiotics, or a combination of both could demonstrate that the healing of DU ulcer was closely related to the clearance of Cp and healing of gastritis. Relapse of DU was closely associated with reappearance of Cp and active chronic gastritis. At the present state the combination of bismuth salts and antibiotics has achieved the highest eradication rates of Cp and thus lowest relapse rates of DU. Antibiotics therefore seem to be an indispensable factor in the antimicrobial treatment of Cp associated diseases.