NO is associated with a variety of physiological and pathological processes. Products of NO, as nitrite, nitrate, nitrotyrosine and nitrosothiols can be detected in EBC, which is collected by a simple, safe and non-invasive technique, are becoming useful tools for monitoring airway infl ammation. The detection of infl ammatory markers in EBC is not yet a clinical tool because few of the variables studied have been demonstrated to have clinical diagnostic or prognostic utility. Prospective studies will need to investigate any potential markers in EBC and compare them with current ‘gold standards’ for diagnosis and disease activity. Nonetheless, by virtue of its non-invasive nature, this technique holds considerable promise. Already on-line measurements of hydrogen peroxide are available and more bedside analyses are likely to become available. Sensitive assays are needed to measure markers in EBC which have low concentrations, and to explore new markers, but this technique will have far-reaching applicability in both research and possibly clinical medicine.