To analyze specific mucosal changes in asthmatic patients receiving long-term, high-dose beclomethazone dipropionate (BDP) inhalation therapy, we performed bronchial mucosal biopsies and immunohistochemical analysis of patients who had been treated with or without BDP-inhalation. Our study enrolled 6 chronic severe asthmatics who were treated with 1,800 micrograms/day or more of BDP with regular use for more than 3 years (HD-BDP group), 6 mild asthmatics who were not treated with BDP (non-BDP group), and 6 control subjects. Specimens of bronchial mucosa were stained with anti-EG 2 (eosinophils), anti-UCHLA-1 (T lymphocytes) and anti-tryptase (mast cells). Although limited eosinophil infiltration was observed in the HD-BDP and control groups, a significant increase was noted in the non-BDP group. The infiltration of both T lymphocytes and mast cells exhibited a statistically significant increase in the non-BDP group compared to the HD-BDP and control groups. In chronic severe asthmatics, airway mucosal cell infiltration was reduced by high-dose and long-term inhaled BDP therapy, and BDP also relieved their asthmatic symptoms. However, in mild asthmatics, bronchial mucosal cell infiltration remained high. For such patients, we concluded that initiating BDP therapy from an early stage may bring clinical improvement and help prevent cell infiltration.