AIMS--To investigate the diagnostic value of mucosal IgA and IgG Helicobacter pylori antibodies. METHODS--The study population comprised 209 consecutive patients with severe dyspeptic complaints referred for upper gastrointestinal endoscopy. A positive culture or histological identification of H pylori in gastric biopsy specimens, or both, were used to confirm infection. Specific IgA and IgG H pylori antibodies were determined using a modified ELISA technique. RESULTS--Of the 209 patients, 137 were infected with H pylori. The diagnostic value of systemic IgA and IgG H pylori antibodies was confirmed. Systemic IgA antibodies had a sensitivity of 76.6% (95% confidence interval 69.5-83.7) and a specificity of 94.4% (89.1-99.7). The sensitivity and specificity for systemic IgG antibodies were, respectively, 97.1% (94.3-99.9) and 98.6% (95.9-100). A moderate but clinically important correlation was found between local and systemic IgA and IgG. Mucosal IgA H pylori antibodies had a sensitivity of 98.5% (96.5-100) and a specificity of 91.7% (85.3-98.1), while for IgG these figures were, respectively, 88.3% (82.9-93.7) and 98.6% (95.9-100). As a diagnostic test mucosal IgA H pylori antibodies were comparable with culture and histology. CONCLUSION--Determination of local IgA and IgG H pylori antibody levels is a highly sensitive and specific test for the diagnosis of H pylori infection.