PURPOSE: To evaluate the lung changes in healthy smokers, as seen on inspiratory and expiratoryhigh-resolution computed tomography (HRCT). MATERIAL AND METHODS: Twenty-seven healthy smokers (light smokers,below 20 pack-years, n=16; heavy smokers, above 20 pack-years, n=11) and 25 nonsmokers underwent inspiratory andexpiratory HRCT. All healthy smokers had normal pulmonary function and chest radiography. Parenchymal andsubpleural micronodules, ground-glass attenuation, centrilobular and paraseptal emphysema, bronchial wallthickening, bronchiectasis and septal line were evalvated on inspiratory scan and by air-trapping on expiratoryscan. RESULTS: On inspiratory scan, parenchymal micronodules were observed in one of 25 nonsmokers(4%), two of 16light smokers(13%) and five of 11 heavy smokers(45%); subpleural micronodules in two(8%), four(25%), two(18%);ground-glass attenuation in 0(0%), one(6%), three(27%); centrilobular emphysema in 0(0%), one(6%), three(27%);paraseptal emphysema in three(12%), 0(0%), five(45%); bronchial wall thickening in 0(0%), two(13%), one(9%),bronchiectasis in 0(0%), one(6%) two(18%) and septal line in one(4%), four(25%), two(18%). On expiratory scan,air-trapping was detected in 0 of 15 nonsmokers(0%), two of 17 light smokers(12%), and five of 11 heavysmokers(45%). Statistically significant differences between these three groups were found in parenchymalmicronodules(P=0.006), ground-glass attenuation(P=0.008), centrilobular emphysema(P=0.018), paraseptal emphysema(P=0.005) and air-trapping(P=0.013) between these three groups. CONCLUSION: According to the findings of HRCT,heavy smokers had higher frequency of parenchymal micronodules, ground-glass attenuation, centrilobular andparaseptal emphysema, and air-trapping than nonsmokers and light smokers.