OBJECTIVE Supraphysiological doses of exogenous glucocorticosteroids cause adrenocortical suppression. Dehydroepiandrosterone sulfate (DHEA-S) is the most abundant adrenal androgen and estrogen precursor. We studied to what extent inhaled glucocorticosteroid therapy for asthma decreases serum DHEA-S concentrations. DESIGN AND METHODS We measured serum DHEA-S and cortisol concentrations in 101 adult patients with newly detected mild asthma before and after 2 and 12 weeks of treatment with inhaled glucocorticosteroids. The patients were randomized to receive budesonide 200 microg/day (low dose group, n=50) or 800 microg/day (high dose group, n=51) in two parallel groups double-blindly. RESULTS In the low dose group, serum DHEA-S concentrations decreased from the baseline by a mean of 8 % (95 % confidence interval (CI), 3-13 %, P<0.01) after 2 weeks of therapy, and by 2 % (95 % CI, 9 % decrease to 5 % increase, NS) after 12 weeks. In the high dose group, the respective decreases were 16 % (95 % CI, 10-21 %, P<0.001) and 18 % (95 % CI, 12-24 %, P<0.001). The difference between the treatment groups was significant at both 2 and 12 weeks. During the 12 week treatment period the baseline concentrations of serum cortisol did not decrease in the low dose group, while in the high dose group the decrease was significant at 12 weeks (P<0.01), but not at 2 weeks. The forced expiratory volume in 1 s improved equally well in both groups. CONCLUSIONS Inhaled budesonide decreased serum DHEA-S concentrations, which may indicate adrenocortical suppression. Reduced adrenal production of androgen and estrogen precursors may increase the risk of osteoporosis especially in postmenopausal women.