Purpose : To separately evaluate the respiratory function of both lungs separately in patients with unilateralmain bronchial stenosis or obstruction, applying respiratory dynamic CT using the spiral technique. Materials andMethods : This study involved five normal subjects and six patients with main bronchial stenosis. Time-continuousscan data at a selected levels during forced vital capacity maneuver were obtained, and static images wereretrospectively reconstructed using 0.67 sec. partial scan data per image. Time-density curves for controls andpatients were plotted and compared. Results : The highest values of mean attenuation were -697$pm$49 H for the leftlung and -684$pm$39 H for the right lung of controls, and -697$pm$55HU for the healthy lung and -791$pm$63H for thediseased lung of the patients. The lowest values were -837$pm$42H for the left lung and -842$pm$35H for the right lungof contorls, and -847$pm$40H for the healthy lung and -858$pm$34H for the diseased lung of patients. Mean durations ofexpiration were 1.64$pm$0.65 seconds for the left lung and 1.58$pm$0.50 seconds for the right lung of controls, and1.66$pm$0.60 seconds for the healthy lung and 1.96$pm$0.49 seconds for the diseased lung of patients. Time-attenuationcurves for the right and left lung of controls were not significautly different, but except for the lowest valueof mean attenuation, these were signficantly different for the healthy and diseased longs of patients. Conclusion: Respiratory dynamic CT is an updated technique which permits imaging of the functional status of lung parenchymaduring respiration. It may be useful in the evaluation and quantification of lung function in patients withproximal airway stenosis.