Traditional methods of sampling secretions from the lower respiratory tract include sputum collection, sputum induction, and bronchoscopy with bronchoalveolar lavage. They cannot be repeated within a short period of time because of their invasiveness, and because the procedures themselves may include an inflammatory response. The need to monitor inflammation in the lungs has led to the exploration of exhaled gases and condensates. Noninvasive monitoring may assist in differential diagnosis of pulmonary diseases, assessment of disease severity and response to treatment.