Action mechanisms of complex spa therapy (swimming training in a hot spring pool, inhalation with iodine salt solution, and fango therapy) were studied in relation to patient age, clinical asthma type, and airway inflammation. Actions of spa therapy were observed by two clinical effects : direct and indirect effects. Improvement of subjective symptoms, ventilatory function, and bronchial hyperresponsiveness was observed as direct effects of spa therapy, and improvement of suppressed function of adrenocortical glands as indirect effects of the therapy. The clinical effects of spa therapy were higher in patients over the age of 40. Regarding clinical asthma type, the effects were larger in patients with type Ib and type II asthma than in those with type Ia. The efficacy of spa therapy was closely related with airway inflammation in patients with type Ib and type II asthma.