Twenty-five patients with intractable asthma had swimming training in a hot spring pool for 3 months. The subjects were divided into three groups according to their clinical symptoms and ages. Changes of ventilatory function during swimming training were observed in in each group. The ventilatory function test revealed that free swimming training in a hot spring pool for 30 min did not induce bronchoconstriction in any of the groups. The values of ventilatory parameters such as FEV 1.0%, %PEFR, %V50 and %V25 were improved after the 3-month swimming training. The improvement of ventilatory parameters, especially %MMF, %V50 and %V25, by the training was most remarkable in the type II asthma group. The percent increase in %MMF, %V50 and %V25 was highest in patients more than 61 years of age, and higher in patients aged 40 to 60 years than in younger patients.