Fifty-two children 6 to 12 yr of age and 37 young adults 13 to 38 yr of age with moderate to severe extrinsic asthma requiring daily bronchodilators and who had been taking beclomethasone dipropionate (BDP) for at least 3 months were evaluated. All patients received their regular daily medications and BDP, 2 inhalations 4 times a day (q.i.d.) (total dose, 336 micrograms/day), for 2 wk; they were then randomized to receive either BDP or placebo aerosol, 4 inhalations twice a day (b.i.d.), with the same total dose/day as well as their regular medications, for 8 wk. Placebo patients deteriorated significantly by comparison with BDP patients in respiratory symptoms and pulmonary functions. More placebo than BDP patients ended participation in the study prematurely because of increasingly severe symptoms. In the 89 study patients, there were no significant differences in respiratory symptoms or pulmonary function measurements between the b.i.d. and q.i.d. dosage regimens in either pediatric or adult age groups. There were no significant changes in mean morning cortisol levels from baseline measurements to the end of the study period; at that time, all patients had a normal ACTH stimulation test. We conclude that BDP (336 micrograms/day) is as effective and safe for control of asthma symptoms with b.i.d. as with q.i.d. dosage schedules in pediatric and young adult patients.