Histamine release from bronchoalveolar cells induced by house dust mite (HDm) was compared in patients with atopic asthma sensitive to HDm in relation to age. 1. Total cell number in bronchoalveolar lavage (BAL) fluid was larger in patients over the age of 40 years (9.10×10(6)) than in those aged between 20 and 39 years (6.25×10(6)), however, this was not significant. 2. Number of BAL eosinophils was not significantly different between the two age groups. 3. Number of BAL basophilic cells was significantly higher in younger patients (20-39 years) (1.85±1.03×10(2)/mℓ) than in older patients (40+ years) (0.39±0.24×10(2)/mℓ) (p<0.001). 4. Histamine release from BAL cells induced by HDm was significantly higher in younger patients (38.1±24.8%) than in older patients (0%) (p<0.001). These results suggest that histamine release from BAL cells in patients with HDm allergy decreases with aging.