Forty children with childhood asthma were conducted through a double-blind cross-over study to compare the effect of 400 micrograms beclomethasone dipropionate administered as aerosol and powder (Rotacaps). Children with severe asthma derived more benefit from the steroid administered as aerosol judged from their peak flow performance in the morning, although neither evening peak flow nor symptom scores revealed any difference. It is concluded that the Rotacaps are an advantageous supplement to available medication for the treatment of asthmatic children, although it should be observed that, using equal amounts of BDP, powder administration seems less effective than aerosol.