Initial treatment of status asthmaticus with corticosteroids caused significant improvement in arterial hypoxemia that did not occur in the control group. This improvement was not dependent upon changes in ventilatory function (FVC, FEV1). Betamethasone, hydrocortisone, and dexamethasone all appeared to have this beneficial effect. Both betamethasone and dexamethasone appeared to have the added advantage of higher unbound (pharmacologically active) corticosteroid levels. No toxic or adverse reactions were noted in this 24-hour study. Thus, corticosteroid therapy is indicated early in treatment of status asthmaticus, as withholding it needlessly exposes the patient to the risks of prolonged hypoxemia.