Helicobacter pylori infects ~ 50% of the world's population and a quarter of the European population. H. pylori is responsible for a large proportion of gastric and duodenal ulcers and gastritis. Chronic infection with H. pylori is a risk factor for the development of stomach cancer and MALT (mucosa-associated lymphoid tissue) Lymphoma. The prospects of success for an antimicrobial eradication therapy is drastically reduced by the significant increase in antibiotic resistance in Austrian H. pylori isolates. The currently available data were obtained however from narrowly defined geographical regions and the clinical routine without information on patient selection. We suspect a considerable geographical variability of resistance patterns and a clinical bias for a preferential investigation of patients with unsuccessful, empirical eradication therapy. The objective of the proposed study is therefore an Austria-wide collection of data on H. pylori resistance in a prospective clinical study. The data thus collected will enable a significant improvement in current treatment recommendations.