Airway hyperresponsiveness to a wide variety of stimuli is a characteristic feature of bronchial asthma. Although its precise mechanism remains uncertain, previous investigations revealed the importance of airway inflammation for the development of airway hyperresponsiveness. Thus, in an experimental animal, the stimuli which induce airway hyperresponsiveness cause airway inflammation simultaneously, and suppression of this airway inflammation attenuates airway hyperresponsiveness. Furthermore, in asthmatic subjects, the level of airway hyperresponsiveness usually correlates with the clinical severity of asthma and medication requirements. Based on these findings, recently, asthma is defined by reversible airway obstruction, airway hyperresponsiveness and airway inflammation. Key concept for management of asthma, therefore, may be focused on monitoring airway inflammation, and on treating this inflammation. In addition to the direct assessment of airway inflammation by induced sputum or exhaled nitric oxide, it can be also reflected by airway hyperresposiveness on peak flow monitoring. For the treatment of asthma, therapeutic interventions with anti-inflammatory agents modify airway hyperresponsiveness, improve asthma symptoms, and reduce the need for frequent use of a bronchodilator.