OBJECTIVE: Fractional exhaled nitric oxide (FeNO), bronchial nitric oxide (JawNO) and alveoar nitric oxide (CNO) are biomarkers of eosinophilic inflammation, usually measured simultaneously with spirometry and bronchodilation. Our aim was to investigate the effect of bronchodilation and spirometry on FeNO, CNO and JawNO in children and young adults with well-controlled asthma and in healthy volunteers.METHODS: FeNO was measured in 95 subjects (62 controls, 33 asthmatics). CNO and JawNO were assessed in 41 of the subjects (35 healthy, 6 asthmatics.) Measurements were performed before spirometry (1), right after spirometry (2), 20 min after the first spirometry and bronchodilation (3), right after the post-bronchodilation spirometry (4) and 30 min after the last spirometry (5).RESULTS: The presence of well-controlled asthma was not associated with different pattern of reaction after spirometry and bronchodilation. A statistically significant difference was observed only between FeNO4 and FeNO5, as well as between CNO1 and CNO3 (19.14 ± 1.68 vs 20.62 ± 1.85 ppb, p = 0.001 and 4.42 ± 0.40 vs 3.09±0.32 ppb, p = 0.001, respectively).CONCLUSIONS: Spirometry and bronchodilation have an insignificant effect on FeNO and JawNO. Even if a slight change occurs in FeNO and JawNO, this does not modify clinician's decision and therapeutic strategy. CNO values (CNO1) are significantly decreased 20 min after spirometry and bronchodilation.