Inhalation radioaerosol lung imaging was performed in 86 patients with chronic obstructive lung disease (COLD) and in 45 asymptomatic smokers with small airways dysfunction. Within certain limits analysis of abnormal aerosol scans helped distinguish emphysematous from brochitic and asthmatic types of disease. Patients with asthma often responded to bronchodilator treatment and abnormal aerosol images reverted to near normal patterns. Besides a slight aerosol distribution inhomogeneity in the lung periphery, patients with small airways dysfunction showed significant hypodeposition of inhaled particles distal to the ciliated airways. Compared with small airways dysfunction, COLD was associated with an even more decreased aerosol penetrance to the alveoli.