Studies with beta2-adrenergic agonists have shown that particle size and total dose are important determinants of optimum bronchodilation. Drug deposition in the airways is probably the most important factor for bronchodilation, since beta2-adrenoceptors and muscarinic M3 receptors are present mainly in the peripheral and central airways, respectively. Furthermore, clinical efficacy can be maintained while minimizing systemic exposure by selecting an appropriate particle size. Changes in lung function provide a means of monitoring the relationship between delivery of the bronchodilator and its efficacy, whereas there is no such immediate means of assessing antiinflammatory preventative therapy such as inhaled corticosteroids. Asthma is primarily an inflammatory disease but there are no simple tests to detect the accumulation of inflammatory cells and mediators. Data are presented to demonstrate the reduction of certain inflammatory markers in bronchial biopsy tissue taken from asthmatic patients after corticosteroid therapy. Measurement of inflammatory markers in both bronchial biopsy tissue and bronchoalveolar lavage samples may provide a way of monitoring the site of action and efficacy of inhaled corticosteroids in the future. Furthermore, it is envisaged that the effect of corticosteroid particle size on efficacy and systemic bioavailability may be investigated by exploiting these methods.