Chronic inflammation in asthma is a key feature of the disease and monitoring is an essential component of asthma management. Inflammation is present in both central and peripheral bronchi and can be measured by non invasive markers, such as fractional exhaled nitric oxide (FeNO). FeNO is increased in asthmatics, as compared to normal subjects and is lowered by inhaled corticosteroids (ICS) with a dose-response relationship that is more evident for asthmatic patients with high levels of FeNO. FeNO measuring is easy to be performed in almost all patients including children and can be helpful as a tool contributing to asthma diagnosis and evaluation of the response to antinflammatory therapy with ICS. Smoking affects FeNO measurements and this has to be considered when evaluating patients with asthma who smoke. The different measurement of bronchial and alveolar FeNO can give information on the distribution of inflammation in the bronchial tree and is of particular interest for clinical pharmacology. Nonetheless, the clinical application of FeNO still needs to be clarified but it is clearly nowadays one of the most used non-invasive markers giving information on the inflammatory component of the disease.

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