Although glucocorticoid is the most effective agent for bronchial asthma, its systemic administration leads to suppression of adrenocortical function. Rapid ACTH test has been performed for assessing the function of the hypothalamic-pituitary-adrenocortical (HPA) system of asthmatics. Recently human corticotropin-releasing hormone (CRH) has been chemically synthesized. In order to evaluate clinical usefulness of CRH, we compared CRH test with ACTH test in 17 patients with bronchial asthma (3 patients out of them concurrently receiving prednisolone 5-10 mg/day). Both tests were carried out within 2 weeks after 6 month treatment with fluticasone propionate (800 micrograms/day) inhaled via pMDI. There is no significant difference between results obtained from the both tests. Thus, dividing subjects into high and low responders based on an extent of increases in plasma ACTH levels after the CRH injection, we found a significant difference in maximal plasma concentrations of cortisol between after CRH and ACTH injections in the low responders. Therefore, in some patients, CRH test provides more accurate assessment of the function of HPA system than ACTH test.