To evaluate the effects of corticosteroids on the resolution of acute attacks of asthma, 38 young, acutely ill, asthmatic subjects were given a single intravenous injection of either 0.25, 0.50 or 1.0 g of hydrocortisone hemisuccinate or a placebo (sterile saline solution) in a random, double blind manner. Each was then treated with isoproterenol, at hourly intervals, for a minimum of six hours, and the serial changes in plethysmography, spirometry, lung volumes, subjective complaints and physical findings that occurred as the patients improved were observed. No statistical differences were found in any of the physiologic or clinical variables between those patients given any dose of steroids and their matched controls. From this it has been concluded that hydrocortisone, in the doses and route of administration employed, does not produce any immediate benefits in the treatment of acute asthma.