Exhaled nitric oxide (NO) is elevated in asthma, but the underlying mechanisms remain poorly understood. Recent results in subjects with asthma report a decrease in exhaled breath pH and ammonia, as well as altered expression and activity of glutaminase in both alveolar and airway epithelial cells. This suggests that pH-dependent nitrite conversion to NO may be a source of exhaled NO in the asthmatic airway epithelium. However, the anatomical location (i.e., airway or alveolar region) of this pH-dependent NO release has not been investigated, and could impact potential therapeutic strategies. We quantified airway (proximal) and alveolar (peripheral) contributions to exhaled NO at baseline and then following phosphate buffered saline (PBS) inhalation in stable (mild-intermittent to severe) asthmatic subjects (20-44 years old, n=9) and healthy controls (22-41 years old, n=6). The mean (SD) maximum airway wall flux (pl.s-1) and alveolar concentration (ppb) at baseline in asthma and healthy controls was 2530 (2572) and 5.42 (7.31), and 1703 (1567) and 1.88 (1.29), respectively. Compared to baseline, there is a significant decrease in the airway wall flux of NO in asthma as early as 15 minutes and continuing for up to 60 minutes (maximum -28% at 45 minutes) following PBS inhalation without altering alveolar concentration. Healthy control subjects did not display any changes in exhaled NO. We conclude that elevated airway NO at baseline in asthma is reduced by inhaled PBS. Thus, airway NO may be, in part, due to nitrite conversion to NO and is consistent with airway pH dysregulation in asthma.