The aim of this. study was to compare the results of low-dose (LDT) and standard-dose (SDT) ACTH tests in the assessment of adrenal function in 30 asthmatic children (mean age 9.35 +/- 1.9 years, 19 boys) who were treated with budesonide Turbohaler at conventional 400 jig or 600 mu g daily doses for 8 weeks by a prospective, randomized, and open parallel study. Budesonide did not lead to any significant suppression of the hypothalamic-pituitary-adrenal (HPA) axis in either treatment group. However, when individual patient values were examined at the end point, peak cortisol concentrations after LDT were below 2 SDs of the pretreatment values in four patients (13.3%). Also, the increment in cortisol values was < 200 nmol/l in all four patients. Decreased 24-hour urinary free cortisol excretion provided further evidence for HPA axis suppression in these patients. Two of these four poor responders to LDT showed normal stimulation with SDT. In conclusion, even with moderate doses and short-term use, adrenal suppression may occur in certain susceptible patients. The low-dose ACTH test is more reliable than SDT for the evaluation. of such patients.