FINDINGS: In vitro measures of antiinflammatory activity of corticosteroids consistently demonstrate potency differences among the various corticosteroids. Traditionally, these in vitro measures have been used to develop new corticosteroids with greater topical activity. While no accepted direct measure of antiasthmatic antiinflammatory activity exists, clinical trials using surrogate measures (., forced expiratory volume in 1 second, peak expiratory flow, bronchial hyperresponsiveness, symptom control) indicate that in vitro measures provide a relatively accurate assessment of antiasthmatic potency. The relative antiinflammatory potency of the inhaled corticosteroids is in the following rank order. flunisolide = triamcinolone acetonide < beclomethasone dipropionate = budesonide < fluticasone. Studies of systemic activity appear to confirm this relative order of potency. Currently, no evidence exists for greater efficacy for any of the inhaled corticosteroids when administered in their relative equipotent dosages. The preponderance of current data suggests that when administered in equipotent antiinflammatory doses as a metered-dose inhaler plus spacer or as their respective dry-powder inhaler, the existing inhaled corticosteroids have similar risks of producing systemic effects.