Measuring of the fraction of nitric oxide (NO) in the exhaled breath (FE NO) at multiple expiratory flows allows assessment of the flow-independent parameters of the two-compartment model for NO exchange in the airways and lung: the alveolar NO concentration, (CANO) and bronchial NO flux (JawNO), respectively. The first aim of the present prospective study was to compare the estimates of CANO and JawNO obtained using the linear regression analysis according to Pietropaoli et al (method P) and Tsoukias et al (method T).