One hundred and twenty four patients with severe asthma requiring maintenance treatment with oral corticosteroids were included in a multicentre, double-blind, randomized study comparing the effects of inhaled beclomethasone dipropionate (BDP) (250 micrograms.puff-1), beginning with 1,000 micrograms daily, vs placebo (P). Pulmonary function was assessed and dosage of prednisone and BDP (or P) were adjusted every 15 days according to a clinical score. Our results showed, after 3 months: 1) A greater drop-out rate in the P group than in the BDP group (36 vs 6%, respectively, p less than 0.01); 2) A total weaning from prednisone in 76% of patients in the BDP group (mean BDP dosage = 1,270 +/- 340 micrograms.day-1, mean +/- SD), vs 34% in the P group (p less than 0.001). The mean daily dosage of prednisone was reduced from 17 +/- 7.5 mg to 3.1 +/- 7.4 mg in the BDP group vs 15.6 +/- 7.7 mg to 9.1 +/- 9.4 mg in the P group (p less than 0.001) without any relationship between the steroid-sparing effect and the initial dosage of prednisone; 3) Mean change in forced expiratory volume in one second (FEV1) was +7 +/- 21% from the initial value in the BDP group vs -6 +/- 20% in the P group; p less than 0.01. Thus, in patients with severe asthma requiring oral corticosteroids, high-dose BDP has an important oral steroid-sparing effect not related to the initial dosage of oral steroids and allows a better control of airway obstruction than oral corticosteroids alone.