Bronchial hyperresponsiveness was examined in relation to age, ventilatory function, and the proportion of bronchoalveolar lavage (BAL) cells in 39 patients with type Ia asthma (simple bronchoconstriction) (25 with type Ia-1 and 14 with type Ia-2), classified by clinical symptoms. 1. The proportion of BAL eosinophils was significantly higher in type Ia-2 than that in type Ia-1 asthma patients. 2. Bronchial reactivity to methacholine was not different between type Ia-1 and type Ia-2 asthma patients. 3. Bronchial hyperreactivity tended to decrease as patient age was higher in both types of asthma. Neither ventilatory function (FEV1.0%) nor the proportions of BAL lymphocytes and neutrophils was not correlated with bronchial hyperresponsiveness in both types of asthma. 4. Bronchial reactivity to methacholine more dereased with the increase in the proportion of BAL eosinophils in both type Ia-1 and Ia-2 asthma patients. The results show that bronchial hyperresponsiveness in patients with type Ia asthma is correlated to patients age and the proportion of BAL eosinophils.