Effects of long-term spa therapy on reduction of the costs of drugs used for the treatment were examined in 23 patients with asthma. The costs of drugs used per patient for 1 year when spa therapy started (1997) were compared with the costs used for 1 year after spa therapy for 3 years (2000). 1. The decrease in the total costs of all drugs was \31, 910 in patients with stage 1, \74, 900 in those with stage 2, \113, 450 in stage 3, and \180, 910 in stage 4. The % decrease of the costs of drugs used was 34.2% in stage 1, 46.3% in stage 2, 37.1% in stage 3, and 42.4% in stage 4. The results showed that the reduction in the costs of drugs tended to increase as asthma severity increased, and that the % decrease of the costs was higher in stage 2 and 4, in which the %decrease was more than 40%. 2. The reduction of costs of each drug, bronchodilators, glucocorticoids, antiallergic agents, mucolytics, and antibiotics after spa therapy, was significant in patients with stage 3 and stage 4, whose severity was considerably increased. However, the decrease in the costs of these drugs after spa therapy was not significant in patients with stage 1 and 2. The reduction of the costs more than 50% was observed in bronchodilators, antiallergic agents, mucolytics, and antibiotics in patients with stage 4, in whom the reduction of the costs of these drugs was significant. The results obtained here suggest that the costs of drugs used for asthma treatment could be reduced by spa therapy in patients with more increased severity.