The adrenocortical function was investigated in 18 children treated with high-doses of inhaled glucocorticoid aerosol (mean: 1965 micrograms/1.73 m2 body surface a day). Basal serum cortisol was only below the normal range in patients treated with doses exceeding 2500 micrograms/1.73 m2 body surface. 15 of 18 children had normal 24 h urinary free cortisol excretion, compared with 27 normal children matched for age, sex and body surface. Three patients taking more than 2400 micrograms/1.73 m2 body surface showed excretion values below the range for the normal controls. 10 of 12 patients showed a normal response to a short ACTH stimulation test. One patient treated with 3300 micrograms/1.73 m2 body surface showed no response and one patient gave a borderline response to ACTH. We concluded that doses up to 2000 micrograms/1.73 m2 body surface/24 can be administered by pressurized aerosol with little risk of adrenocortical suppression.