Airway inflammation plays an important role in diseases such as asthma and chronic obstructive pulmonary disease. The use of non-invasive techniques for the evaluation of these inflammatory diseases has been the object of increasing interest in the past few years. The collection of expired breath condensate is achieved by freezing the exhaled air with the use of special condensing devices and provides useful information about areas of the respiratory tract accessible exclusively with invasive techniques in the past. In the exhaled breath condensate there have been measured molecules, such as hydrogen peroxide, 8-isoprostane, end products of NO metabolism (nitrites/nitrates, nitrotyrosine), leukotrienes and recently pH. These measurements have clinical application in many inflammatory diseases of the respiratory tract, such as asthma, chronic obstructive pulmonary disease, cystic fibrosis, bronchiectasis and ARDS. Despite the methodological problems of this procedure, its non-invasive nature gives the opportunity for repeated measurements on the same person and provides valuable information for the assessment of airway inflammation. Pneumon 2001, 14(3):184-196.