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 AND METHODS: This study involved five normal subjects and six patients with main bronchial stenosis. Time-continuous scan data at a selected levels during forced vital capacity maneuver were obtained, and static images were retrospectively reconstructed using 0.67 sec. partial scan data per image. Time-density curves for controls and patients were plotted and compared. RESULTS: The highest values of mean attenuation were -697±9 H for the left lung and -684±9 H for the right lung of controls, and -697±5HU for the healthy lung and -791±3H for the diseased lung of the patients. The lowest values were -837±2H for the left lung and -842±5H for the right lungof contorls, and -847±0H for the healthy lung and -858±4H for the diseased lung of patients. Mean durations ofexpiration were 1.64±.65 seconds for the left lung and 1.58±.50 seconds for the right lung of controls, and1.66±.60 seconds for the healthy lung and 1.96±.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 value of 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 parenchy maduring respiration. It may be useful in the evaluation and quantification of lung function in patients with proximal airway stenosis.