Rationale: The aim of the present study was to analyze how models currently used to distinguish alveolar from bronchial contribution to exhaled NO are affected by manipulation of NO formation in the pharyngo-oral tract. Methods: Exhaled NO has been measured at multiple flow-rates in 15 healthy subjects in two experiments: the first with measurements at baseline and 5 min after chlorhexidine (CHX) mouthwash, and the second with measurements at baseline, 60 min after ingestion of 10 mg NaNO₃ / kg body weight and 5 min after CHX mouthwash. Alveolar NO concentration (Calv_NO) and bronchial flux (J'aw_NO) were calculated using the slope-intercept model with or without adjustment for trumpet shape of airways and axial diffusion (TMAD). Salivary nitrate and nitrite were measured in the second experiment. Results: Calv_NO (median (range)) was reduced from 1.16 ppb (0.77, 1.96) at baseline to 0.84 ppb (0.57, 1.48) 5 min after CHX mouthwash (p<0.001). The TMAD-adjusted Calv_NO value after CHX mouthwash was 0.51 ppb (-0.20, 0.91). The nitrate load increased J'aw_NO from 32.2 nL/min (12.2, 60.3) to 57.1 nL/min (22.0, 119) in all subjects and Calv_NO from 1.47 ppb (0.73, 1.95) to 2.91 ppb (1.33, 7.20) in subjects with high nitrate turnover (>10-fold increase of salivary nitrite after nitrate load). The CHX mouthwash reduced the Calv_NO levels to 1.18 ppb (0.72, 2.07) in these subjects with high nitrate turnover. All these results remained consistent after TMAD adjustment. Conclusion: Estimated alveolar NO concentration is affected by the pharyngo-oral tract production of NO in healthy subjects, with a decrease after CHX mouthwash. Moreover unknown ingestion of dietary nitrate could significantly increase estimated alveolar nitric oxide in subjects with high nitrate turnover, and this might be falsely interpreted as sign of peripheral inflammation. These findings were robust for trumpet shape of airway tree and axial diffusion.