Colonization of the gastric mucosa by Helicobacter pylori is the major cause of gastroduodenal pathologies in humans. Studying the outcome of the humoral immune response directed against this gastric pathogen may contribute substantially to vaccine development and to the improvement of diagnostic techniques based on serology. By using two-dimensional gel electrophoresis, 29 proteins from H. pylori G27 were identified which strongly react with sera derived from H. pylori-infected patients suffering from different gastroduodenal pathologies. These antigens were characterized by mass spectrometry and proved to correspond to products of open reading frames predicted by the H. pylori genome sequence. The comparison of the antigenic patterns recognized by these sera revealed no association of specific H. pylori antigens with antibodies in patients with particular gastroduodenal pathologies.