Exhaled NO (FE(NO)) measurements have been utilized as a marker to diagnose asthma as well as a non-invasive tool for monitoring airway inflammation and the response to anti-inflammatory medications. One area where this non-invasive monitoring may be helpful is for asthmatic athletes as they train for competitive events. We hypothesized that in the course of training an asthmatic individual may experience worsening of lung inflammation reflected in FE(NO) levels that may be too subtle to detect by conventional methods like spirometry. Data were collected from an asthmatic patient (n = 1) over the course of endurance training using both the desktop (NIOX) and the portable NO (MINO) analyzers daily for eight weeks. We found that average NO levels measured in the desktop system correlated well with the two portable analyzers (r(2) =0.73, r(2) = 0.74 p < 0.0001); additionally, there was a strong correlation between the two MINO devices (r(2) = 0.88; p < 0.0001). A strong negative relationship existed between the number of miles run and NO, regardless of the device used. FEV(1) and PEF, however, did not change significantly as the miles run increased. Exercise training in asthmatics was associated with a decrease (improvement) in NO levels but no significant change in FEV(1) and PEF. This suggests that exhaled NO levels may be more sensitive to changes in the airway as a result of exercise than traditional pulmonary function testing.