Invasive techniques have been extensively used for the diagnosis of respiratory diseases. Among them bronchoscopy is the most common. In the past few years an increasing interest has been focused on the application of non invasive techniques as a tool in the diagnostic procedure of airway diseases. Among them, induced sputum has received much attention. Airway inflammation plays an important role in the pathogenesis of airway diseases such as asthma and chronic obstructive pulmonary disease. Induced sputum has been used in the evaluation of the inflammatory process but significantly less in the diagnostic procedure. However, the clarification of pending methodological problems and mainly the non invasive nature of the procedure is very promising in terms of using induced sputum for the diagnostic assessment of respiratory diseases. Pneumon 2005, 18(1):53-61.