Adverse side effects of steroid therapy were investigated in 32 asthmatic patients. Thirty-two patients were classified into three groups according to steroid therapy for the past five years; group 1 has been treated with continuous steroid therapy, group 2 with occasional steroid therapy and group 3 without steroid therapy. The results were as follows. 1. Group 1 showed a low level of serum cortisol at 8-9 a. m. The serum concentration of cortisol in patients with daily steroid regimen was lower as compared to that in patients with alternateday steroid therapy. 2. The daily profile of serum cortisol was low in the steroid dependent asthmatic patients, and little increase of serum cortisol level after the administration of prednisolone was shown in group 1. 3. Serum IgG and IgM levels were significantly low in steroid dependent asthmatic patients. 4. The level of serum potassium was low in group 1.