Five severe bronchial asthma patients with glucocorticoid therapy have had free swimming training in the hot spring pool at Misasa Medical Branch. The clinical effect of the swimming training was evaluated after 3 months' training. 1. A slight increase in pulse rate and blood pressure was observed immediately after 30 minutes, swimming, although no significant increase in the two parameters was shown 30 min. after the training. 2. No significant fall in ventilatory function tests such as % FVC, FEV(1.0)%, V(50) and V(25) was demonstrated following the swimming training in a hot spring pool. The results suggest that the free swimming training in a hot spring pool does not induce bronchoconstriction. 3. Clinical efficacy of the swimming training on bronchial asthma was evaluated according to a treatment score, an attack score and an asthmatic score. These scores were decreased during the swimming training. The results obtained in this study showed that free swimming training in a hot spring pool is one of the most suitable therapies for severe bronchial asthma patients.