Twenty eight patients with chronic asthma took part in a double blind single crossover controlled trial of inhaled budesonide and inhaled beclomethasone dipropionate, using high doses of 1600 micrograms and 1500 micrograms daily respectively. Both drugs were administered by pressurised aerosol inhaler; the inhaler containing budesonide and its matching placebo were fitted with a collapsible spacer device. There was no significant difference in the control of asthma during the two six week treatment periods. There was no significant difference in FEV1 and forced vital capacity after four and six weeks of treatment or in mean morning and evening peak expiratory flow rates for the last 21 days of treatment. There was a small but statistically significant reduction in the daytime wheeze score while they were taking high dose budesonide but there was no difference for daytime activity, cough, and night symptoms. The mean basal cortisol concentrations were significantly lower after six weeks of high dose treatment than before treatment (budesonide p less than 0.01, beclomethasone p less than 0.05). There was no difference between mean basal cortisol values after six weeks of high dose treatment, and there was no effect on the rise of cortisol obtained after a short tetracosactrin test. High dose inhaled corticosteroids produced few side effects and were well tolerated.