Nitric oxide (NO) plays an important role in the regulation of smooth muscle tone of pulmonary blood vessels and bronchi. NO is well known for mediating vasodilation and it is involved in control of vascular tone related to cardiovascular diseases, inhibition of platelet aggregation and platelet adhesion, and is also a diffusible signaling molecule which acts as a neurotransmitter [1,2]. Although NO participates in a variety of physiological processes, excess or decreased NO production will have detrimental effects such as an abnormal response to infl ammation and injury, hypo- or hypertension [3,4]. An important role of NO in the lung is non-specifi c host defense and antimicrobial activity against various pathogens. An increase in NO may be due to activation of inducible NO synthase (iNOS) expressed by epithelial cells in response to proinfl ammatory cytokines and oxidants. Viral infection of epithelial cells also increases NO production, and the elevation in NO may limit infection by inhibition of viral replication and mediate the antiviral effect of interferon-g [5,6]. In addition, non-infectious diseases of the airway such as asthma are associated with increased iNOS expression and exhaled NO . Monitoring infl ammatory diseases in the lung can be performed by invasive methods, but newer approaches are generating insights into the applicability of non-invasive techniques. Exhaling through a cooling system generates exhaled breath condensate (EBC) as the breath is saturated with water vapour. It contains volatile and non-volatile substances including nitrite/nitrate as end products of NO metabolism, which can be used to monitor infl ammatory lung diseases.