Costs of drugs used for the treatment for 1 year were examined in 32 pa-tients with asthma in relation to disease severity. Asthma severity was classified as : 1) intermiitent; 2) mild persistent; 3) moderate persistent; 4) severe persistent. 1. The total cost of drugs used for each patient for 1 year was the highest (￥263,710) in patients of stage 4 (severe persistent) and the lowest (￥74,670) in those of stage 1 (intermittent). The costs of bronchodilators and antiallergics were predominant at all stages, and their cost increased significantly with increasing severity. 2. The costs of drugs such as antiallergics and bronchodilators were predominant, and the costs of drugs such as inhaled corticosteroids and mucolytics were considerably high in pa-tients of all stages. 3. The costs of bronchodilators, inhaled corticosteroids, and antiallergics were the largest in patients of stage 4. The results suggested that the costs of durgs used for the asthma treatment tended to increase as the disease sever-ity became stronger from stage 1 to stage 4, and the maln drugs related to the in-crease in total costs were bronchodilators, antiallergics, and inhaled corticosteroids.