Forty one patients (21 women and 20 men aged 35 to 45 years), with bronchial asthma were divided into two groups: those treated with glucocorticoids (with an equivalent daily dose of 8 mg prednisone) and those receiving no glucocorticoid preparations. The control group consisted of 27 healthy volunteers. The diurnal rhythm of serum melatonin, ACTH and cortisol was evaluated in all subjects. It was found that the dysfunction and reduced reactivity of the pituitary-adrenal axis in asthmatics receiving chronic glucocorticotherapy was accompanied by suppressed melatonin rhythm.