The influence of aging on the pathophysiology of asthma in the elderly was examined in 40 patients (20 younger asthmatics under the age of 50 years, mean age 32.5 years and 20 elderly asthmatics over the age of 70 years, mean age 74.3 years), relating to IgE - mediated allergy, pulmonary function, low attenuation area (LAA) of the lungs on HRCT, and the generation of leukotrienes B4 (LTB4) and C4 (LTC4) by leukocytes. The frequency of patients with serum IgE of more than 200 IU/ml, and the incidence of those with a positive RAST score for inhalant allergens were significantly higher in younger patients than in elderly subjects. The values of % FVC, % FEV1 and FEV 1% were significantly larger in younger patients compared with elderly subjects. The % RV was significantly larger in elderly patients than in younger patients, however, the difference in % DLco was not significant between the two age groups. The LAA of the lungs on HRCT and the ratio of expiratory LAA (exp LAA) to inspiratory LAA (ins LAA) were also significantly larger in elderly asthmatics than in younger subjects. The generation of LTB4 and LTC4 was larger in younger patients than in elderly subjects, and LTB4 generation was significantly larger in younger subjects compared with elderly subjects. These results suggest that changes in IgE-mediated allergy, airflow and lung volume accompanied with hyperinflation are often observed in elderly asthmatics.