Clinical significanoce of airway inflammation was assessed in 28 patients with bronchial asthma, and the results were compared with those in 9 patients with chronic obstructive bronchiolitis (COB). 1. Total cell number in bronchoalveolar lavage(BAL) fluid was markedly increased in patients with COB (51.0×10(6)), which was significantly greater than that in those with bronchial asthma (9.6×10(6) ). 2. The proportion of BAL macrophages was significantly higher in patients with bronchial asthma than in those with COB. However, the, absolute number of BAL macrophages was not significantly different between them. 3. The proportion of BAL lymphocytes was higher in patients with bronchial asthma than in those with COB, but this difference was not signifcant. In contrast, the absolute number of BAL lymphocytes was significantly greater in patients with COB than in those with bronchial asthma. 4. The proportion and the number of BAL neutrophils were markedly increased in patients with COB compared to those with bronchial asthma. 5. The proportion and the number of BAL eosinophils were higher in patients with bronchial asthma than in those with COB, although these defferences were not significant. The results suggest that airway inflammation in bronchial asthma is not so intensive as that in COB.