Airway inflammation plays a central role in the pathophysiology of chronic obstructive pulmonary disease. Exposure to cigarette smoke induces the recruitment of inflammatory cells in the airways, which in turn produces various cytokines, chemokines, proteases and pro-inflammatory mediators leading ultimately to increased oxidative stress, a protease/anti-protease imbalance and progressive lung tissue injury. Biomarkers may be useful in monitoring airway inflammation and oxidative stress, defining different phenotypes of the disease and evaluating the response of therapies. Exhaled breath condensate collection is a simple and completely non-invasive method of sampling the lower respiratory tract in humans. Exhaled breath condensate may be a rich source of pulmonary biomarkers including hydrogen peroxide, cytokines, metabolites of the arachidonic acid, nitric oxides and the pH. However, the concentration of these biomarkers is often very low, which may cause several problems in their detection. The clinical applicability of exhaled breath condensate biomarkers cannot be assessed until methods of sample collection and analysis have been standardized.