The relative prednisolone-sparing effects of inhaled budesonide 400 micrograms daily and beclomethasone dipropionate (BDP) 400 micrograms daily were compared in a double-blind crossover study of 26 patients with chronic asthma requiring treatment with BDP and oral prednisolone in a daily dose of 5 mg or greater. During each period of the trial budesonide and BDP were inhaled via conventional pressurized inhalers in a dose of 100 micrograms four times daily. Prednisolone was reduced by 1 mg per month from the patient's normal maintenance dose to zero or to the point at which asthmatic symptoms became unacceptable. The mean reduction in prednisolone dose during BDP treatment was 2.65 mg compared with 1.8 mg at the end of the budesonide period. The difference between the prednisolone-sparing properties of BDP and budesonide assessed in this way in this group of patients was statistically significant in favour of BDP. The mean minimum prednisolone doses at the end of the treatment periods were 3.46 mg for BDP and 4.3 mg for budesonide. Since inhaled steroids were not withdrawn the absolute prednisolone-sparing properties of the two drugs were not assessed, and thus a pharmacological potency ratio cannot be derived from the results. It is concluded that BDP is marginally more potent than budesonide in its prednisolone-sparing properties.