Clinical features of asthma patients with a low % FVC (<75%) were studied in relation to clinical asthma type and disease severity. 1. The value of % FVC was not related to patient age. 2. A significant association between % FVC value and clinical asthma type was found. The value of % FVC was significantly lower in subjects with type Ⅱ asthma (bronchiolar obstruction) than in those with type Ia-1 and type Ia-2 (simple bronchoconstriction) (p<0.001). 3. % FVC value significantly correlated with disease severity. The value in the subjects tended to decrease as their asthma conditions were more severe. 4. The % FVC value in the subjects was improved after treatment (complex spa therapy). These results demonstrate that a significant correlation is present between low % FVC and disease severity in asthma patients with a low % FVC.