- BACKGROUND: Helicobacter pylori (H. pylori) produces large amounts of ammonia. Based on higher readings obtained with an ammonia-sensitive electrode when compared to a specific enzymatic assay, it has been claimed that H. pylori also produces potentially toxic volatile amines. METHOD: We measured ammonia concentrations (NH3) in gastric aspirates from 11 H. pylori positive subjects (22-40 y, 6 M), using an ammonia electrode sensitive to ammonia and amines, and an enzymatic assay specific for ammonia. Continuous aspiration was performed overnight and 220 aspirates were analyzed before and 6 weeks after cure of H. pylori. Gastric samples were diluted 1:3 (before cure) and 1:1 (after cure) according to dilution curves constructed prior to the assays. RESULTS: Median (95% CI) NH3 detected by the electrode/enzymatic assay were 4.34 mM[4.12-4.61]/4.50 mM [4.28-4.68] (p > .05) before cure and 0.54 mM[0.42-0.60]/0.73 mM[0.71-0.81] after cure (p > .05). Intra-class correlation coefficient between the two methods was 0.91 before cure and 0.90 after cure (p < .001). Without dilution, the enzymatic assay was linear for NH3 from 0.01 to 1 mM and saturated at 2.5 mM; the electrode was linear for NH3 from 0.01 to 20 mM. When appropriate dilutions were performed, the enzymatic assay was accurate for NH3 greater than 2.5 mM. CONCLUSION: In subjects with H. pylori infection there is a high NH3 in gastric juice; production of volatile amines appears to be negligible in vivo. An ammonia-sensitive electrode and a specific enzymatic assay are both suitable methods for determining NH3 in the gastric juice of subjects with H. pylori infection.