The safety of inhaled corticosteroids in the treatment of chronic asthma has been questioned. In a prospective crossover study asthmatic children not controlled on other medications were commenced on beclomethasone dipropionate (BDP) or budesonide (BUD), both administered at the dose of 200 micrograms twice per day for 2 wk each in randomized order. Recordings at home included twice daily symptom scores, peak expiratory flow readings, and the use of additional antiasthma medications. Before and after each treatment period the patients were admitted for overnight blood sampling for cortisol, ACTH, and growth hormone, 24-h urine collections for cortisol, and detailed lung function tests. A total of 12 children completed the study. The nocturnal serum cortisol production was significantly reduced by 27 and 35% after 2 and 4 wk of treatment (p = 0.005, p = 0.004; Wilcoxon test), and the urinary free cortisol showed a similar reduction of 33 and 48% (p = 0.023, p = 0.005). Such suppression could be shown on both drugs, BDP and BUD, and there was no significant difference between them. The ACTH and growth hormone values were not significantly changed on any treatment. Lung function tests showed an impressive improvement in FVC, FEV1, FEF50, and FEF25 after 2 wk of treatment regardless of the medication. Differences in lung function improvements between the two drugs were very small and not of clinical relevance. The observations indicate that even low-dose inhaled corticosteroids in the form of BDP or BUD have a systemic effect, which emphasizes the importance of using the minimum dose compatible with good control of asthma.