Fasting breath nitrous oxide (N2O) concentration was determined in relation to pH, nitrate (NO3-) and nitrite (NO2-) concentrations in gastric juice, and Helicobacter pylori infection in 86 successive patients. N2O was measured with an infrared-photoacoustic analyzer. NO3- and NO2- were measured using the Griess reaction. Fasting breath N2O concentration in controls (87 +/- 21 ppb) was not significantly different from that in patients with gastric ulcer or other gastric lesions. Breath N2O was significantly correlated with gastric NO3- (P < 0.01) and was higher in patients with elevated gastric NO2- (246 +/- 87 ppb) than in patients without NO2- (75 +/- 13 ppb). Breath N2O did not differ significantly between subjects who were positive or negative for H. pylori. In conclusion, fasting breath N2O concentration is in some manner related to intragastric NO3- and NO2- concentrations. The possible use of measuring breath N2O as predictors of cancer needs further research.