Children mortality in the context of respiratory disease is estimated at 31.3% from the total of 18.4‰ in Romania (IOMC/UNICEF study in 2005). Functional diagnosis is extremely important for the pneumologist to initiate and monitor a proper treatment. Functional respiratory tests are: 1.Peakflowmetry (PEFR- extremely useful in bronchial asthma especially in controlling asthmatic children), 2. Spirometry (measuring flow, volume expired, pulmonary volumes- CV, VER, VIR, VR, VC, pulmonary capacity, expiratory flows and very useful to evaluate the degree of obstructive disfunction), 3. Pletismography and dilution tests (complete the measurements regarding pulmonary volumes). A second category of pulmonary tests is represented by: 1.exhaled breath condensate measuring volatile compounds (ethanol, hydrogen peroxide) and biological factors (citokynes, surfactants, serotonin, leucotriens) and 2. Exhaled oxidic nitrate (FeNO) predictive for corticotherapy response. This article is a review of this methods regarding their applications, limits, and usefulness.