Ventilatory function and inflammatory cells in airways were compared between patients with type Ⅱ (bronchiolar obstruction) asthma and those with obstructive bronchiolitis. 1. Age and age at onset were higher in patients with type Ⅱ asthma than in those with obstructive bronchiolitis. IgE-mediated allergic reaction was observed in patients with type Ⅱ asthma, but not in those with obstructive bronchiolitis. 2. In ventilatory function tests, all ventilatory parameters examined were lower in patients with type Ⅱ asthma compared to those with obstructive bronchiolitis, and the differences were significant in FEV1.0% (p<0.001), % MMF (p<0.02), and V50 (p<0.01). 3. The proportion of BAL neutrophils was very high in type Ⅱ asthma (55.7%) and obstructive bronchiolitis (74.4%), however, this was not significant. 4. Absolute numbers/BAL fluid of total cells, BAL macrophages and BAL neutrophils were significantly higher in patients with obstructive bronchiolitis than in those with type Ⅱ asthma. 5. The results on absolute number/mℓ of BAL cells demonstrated that number of BAL neutrophils markedly larger in patients with obstructive bronchiolitis compared to those with type Ⅱ asthma. These results show that high proportion of BAL neutrophils was observed in the two respiratory diseases, however, the degree of inflammation in airways was markedly greater in obstructive bronchiolitis.