Airway obstruction and airway hyperresponsiveness are important features of asthma and chronic obstructive pulmonary disease (COPD). Both diseases are characterized by airway wall and lung tissue inflammation, and in asthma there exists a relationship between the inflammatory state of the airways and the severity of hyperresponsiveness. However, the type and cause of this inflammation, as well as the extent and consequences of the inflammatory process, are different in asthma and COPD. Inflammatory processes affecting the airway wall both in peripheral and central areas of the lung appear to be important, the former one dominating in COPD and the latter in asthma. However, it is not clear which structural changes are open for therapy and which are not. Therefore, a better understanding of the consequence of inflammation for lung tissue and airway wall changes in asthma and COPD has to evolve before a full understanding of airway hyperresponsiveness will emanate.