It has now become apparent that asthma, even in its mildest clinical manifestation, is a chronic inflammatory condition of the airways. There have been important advances in understanding the special features of inflammation in asthmatic airways and the role of critical inflammatory cells such as mast cells (important in the acute inflammatory response) and eosinophils, macrophages and T-lymphocytes (involved in the chronic inflammatory response). Many inflammatory mediators have been implicated in asthma, and the development of mediator antagonists suggests that sulphidopeptide leukotrienes may play an important role in bronchoconstrictor responses. Cytokines released from many different cells in the airways are likely to be important in orchestrating and perpetuating the chronic inflammatory response. Chronic inflammation has effects on airway vessels, mucus secretion, smooth muscle and nerves, with evidence to suggest that there are structural changes which may lead to persistent airway abnormalities. The therapeutic implication of these new discoveries is that much earlier use of anti-inflammatory treatments (such as inhaled steroids) is preferable to reliance on bronchodilators which do not control the underlying inflammatory process.