Monitoring of asthma and COPD patients is usually based on symptom scores, use of rescue medication and measurement of lung function. However, both asthma and COPD are chronic inflammatory diseases of the airways and there is a need to assess and monitor inflammation using markers directly implicated in the inflammatory process. Several invasive (bronchoscopy, nasal and skin biopsies) and non-invasive (bronchial hyperresponsiveness, blood, urine, induced sputum, exhaled air) biomarkers have been examined as potential markers of airway inflammation for the diagnosis and follow-up of asthma and COPD patients. The advantages and disadvantages of each one of them are discussed in this review. Presently, available data support the use of bronchial hyperresponsiveness (BHR) and sputum induction as the best available biomarkers to guide treatment in the majority of asthmatic patients, whereas in COPD patients none of the available inflammatory markers has gained wide acceptance among investigators till now. Larger and longer-term population-based studies focused on the relationship between markers of inflammation and treatment regimens are needed to determine the optimum biomarker for any given treatment. Pneumon 2004, 17(3):232-241.in