Corticosteroids have been used in the therapy of acute, severe asthma since the early 1950s. Numerous randomized, double-blind, placebo-controlled trials in adults and children have proven corticosteroids to be efficacious. Only the results from less rigorously designed trials have failed to show a beneficial effect. The onset of response, dose, and mode of administration have been relatively well defined; however, other aspects (i.e., duration of therapy, need to taper the dose, and risks of multiple short bursts) require further study. Early institution of corticosteroids in well-defined patient populations will decrease the need for hospitalizations. However, administration of corticosteroids to every patient presenting to the clinician's office or emergency room prior to aggressive bronchodilator therapy is unwarranted. All patients demonstrating an incomplete response or the inability to maintain a complete response following one to two hours of aggressive bronchodilator therapy should receive a course of corticosteroids. Courses as short as three to five days have proven efficacy in outpatients, whereas hospitalized patients usually are treated for seven to ten days. The duration of therapy depends on the individual rate of response.