One hundred subjects answered a respiratory questionnaire and underwent a physical examination, tests of pulmonary function, and three radionuclide lung-imaging procedures. The results of the radionuclide procedures were compared with each other and with pulmonary function tests and other diagnostic findings to determine their relative sensitivity for detecting evidence of early obstructive airway disease. Perfusion lung imaging was less sensitive than most of the other diagnostic tests evaluated. The aerosol and xenon lung-imaging procedures revealed abnormalities with approximately the same frequency as each other, but more often than any one group of pulmonary function tests, including spirometric data, maximal expiratory flow-volume curves, alveolararterial oxygen gradient, or indices derived from single-breath nitrogen washout. We concluded that xenon and aerosol lung-imaging studies are sensitive and useful screening procedures for detecting evidence of early localized obstructive airway disease and for locating regional abnormalities in the airways of patients with respiratory disease.