Inhaled corticosteroids are now recommended for the majority of patients with asthma. Although their therapeutic ratio is superior to that of oral corticosteroids, their long term use is associated with several potentially important adverse effects. A number of studies have compared the efficacy and/or systemic activity of the currently available inhaled corticosteroids, but the results of many of these studies have been conflicting. Although there are a number of factors that may explain these conflicting results, there is evidence that the type of individuals being studied is important. Extrapolation of the findings from healthy individuals to patients with asthma appears to be misleading because the systemic effects of some, but not all, inhaled corticosteroids are greater in healthy individuals than in patients with asthma.