Purpose : We applied spiral CT to evaluate the dynamic changes of regional ventilation of the lung in normalsubjects and abnormal patients. Materials and Methods : This study includes normal subjects (n=5) and patientswith chronic obstructive pulmonary disease (n=4), small air-way disease (n=3), diffuse panbronchiolitis (n=4), andtracheobronchial tuberculosis (n=2). Time-continuous scan data at a fixed level during forced vital capacitymaneuver(10-12 seconds) were obtained and images were reconstructed retrospectively by using 0.67 second scan dataper image. The reconstructed images were displayed in a cine mode. Time-density curves were plotted and werecorrelated with clinical diagnosis. Results : in normal subjects, mean attenuation difference between fullinspiration and full expiration was 145. 8HU and mean time interval between 20% expiration and 80% expiration was2.04 seconds. in chronic obstructive lung disease, mean attenuation difference between full inspiration and fullexpiration was 21.2HU and mean time interval between 20% expiration and 80% expiration was 3.63 seconds. In smallair-way disease, mosaic-pattern hyperlucency and normal portion of lung showed mean attenuation differencesbetween 20% expiration and 80% expiration to be 49.8HU and 167.0HU, respectively. In diffuse panbronchiolitis,centrilobular region and normal portion of lung showed mean attenuation differences between 20% expiration and 80%expiration to be 35.4HU and 79.3HU, respectively. Conclusion : Respiratory dynamic CT is an updated techniquewhich enable imaging of the functional status of the lung parenchyma. It may be useful in differentiation andquantitation of variable obstructive lung diseases.