In a double-blind cross-over study of 12 asthmatic patients the effects of 1,000 micrograms.day-1 beclomethasone dipropionate (BDP) on airway function, bronchial reactivity and hypothalamic-pituitary-adrenal (HPA) axis have been compared to those of 15 mg.day-1 oral prednisone (PRD). None of the patients had ever received corticosteroids before. Fourteen days treatment with either of both steroids improved airway function, both subjectively and objectively. Both steroids slightly reduced the responsiveness to histamine. PRD suppressed the corticotrophin-releasing factor (CRF) stimulated cortisol release more than BDP did, whereas there was no significant change in adrenocorticotrophic hormone (ACTH) release. The results indicate that short-term treatment with 1,000 micrograms.day-1 BDP reduces bronchial hyperreactivity (BHR) in asthmatic patients, whilst having subtle effects on HPA axis.