The proportions of cells in bronchoalveolar lavage (BAL) fluid, the release of histamine, leukotrienes C(4) and B(4) from leucocytes and BAL cells, and bronchial reactivity to methacholine were examined in 40 patients with asthma in relation to patient age. 1. The proportions of lymphocytes and neutrophils in BAL fluid were higher in older patients over age 60 than in younger patients between 20 and 49. The proportions of eosinophils and basophilic cells in BAL fluid were higher in younger patients than in older patients, and the difference in the proportion of BAL basophilic cells was significant between the two groups (p<0.05). 2. The release of histamine from BAL cells was significantly higher in younger patients than in older patients (p<0.001). The release of LTC(4) from BAL cells was higher in older patients compared to younger patients. 3. Bronchial reactivity to methacholine was higher in younger patients than in older patients. The number of patients reactive to low concentration of methacholine (390μg/mℓ or less) was larger in younger patients (12/16 ; 75.0%) than in older patients (5/14 ; 35.7%). These results suggest that bronchial hyperresponsiveness changes with aging, accompanied by changes in the release of chemical mediators from BAL cells and in the proportion of BAL cells.