The authors studied gastric juice ammonia and urea nitrogen levels to determine how they are altered by gastric Campylobacter pylori (CP) infection. Patients with chronic gastritis (20), peptic ulcer (24), hepatic cirrhosis (10), chronic renal failure (13), or gastric remnant (20) were included. Endoscopic biopsy specimens stained with the Warthin-Starry stain were evaluated for the presence of CP. Blood and gastric juice analysis was performed for 11 of the patients with chronic renal failure and 37 patients from the remaining groups. CP was identified in gastric biopsies from 50 of 87 (57.5%) patients, including 87.5% with peptic ulcer and 40-50% of those with chronic gastritis, cirrhosis, chronic renal failure, or gastric remnant. CP infection had no effect on blood urea nitrogen or blood ammonia levels in any group of patients. The urea nitrogen level of gastric juice was higher in patients with chronic renal failure than in other groups but was not related to CP infection. CP infection was associated with a significant increase in gastric juice ammonia levels, both in patients with chronic renal failure (23.3 mmol/L vs. 2.90 mmol/L; [P less than 0.05]) and in other groups (5.48 mmol/L vs. 1.26 mmol/L [P less than 0.0001]). The authors conclude that elevation of gastric juice ammonia level is an indicator of gastric CP infection.