A DOUBLE-BLIND study on the effect of betamethasone sodium phosphate in the treatment of 297 infants and children with acute bronchiolitis was conducted at five hospitals from December 1963 to June 1965. For this study, the investigators designed a common protocol and standard case report forms for use at the five collaborating centers. The information obtained permitted an evaluation of the effects of the corticosteroid in bronchiolitis and provided further insight into the natural history of the disease. The study was not designed to explore the causes of bronchiolitis or the effect of supportive treatment. In recent years, corticosteroids have been used in the treatment of bronchiolitis on the hypothesis that their anti-inflammatory action would reduce bronchiolar inflammation and swelling. These drugs have been regarded as ineffective by some investigators and lifesaving by others. In 1964, Sussman et al1 reported no change in the clinical course of 49 bronchiolitic