Purpose: Spirometric gating quantitative CT, PULMO-CT, is an objective method for the measurement of pulmonary parenchymal attenuation at a constant level of inspiration. In order to obtain a normal value for quantitative CT of the lung, the authors therefore used PULMO-CT to evaluate the lung density of healthy Koreans with different respiratiory status. Materials and Methods: Twenty healthy Korean volunteers, 18 men and 2 women, ranging in age from 24 to 27 years and with normal chest radiography, were evaluated using the PULMO-CT option of Somatom Plus(Siemens, Erlangen, Germany). Spirometric gating HRCT images, at levels of 50% and 20% of vital capacity, were obtained at the level of the tracheal carina and at 5cm above and below this point. The images were analyzed by semiautomatic programs and the results were evaluated using the Student t-test. Results: The mean attenuation value of lung parenchyma at 50% of vital capacity was -791HU$pm$27.1 and at 20% was -700HU$pm$42.9. The difference in lung attenuation was 91HU and was statistically significant(p<0.001). The for 58.9% of participants, the highest reading for of lung attenuation at 50% of vital capacity was between -899HU and -800HU, and for 20.3% of participants, this reading was between -799HU and -700HU. At 20% of vital capacity, the largest proportion of participants(43.8%) had a reading of between -799HU and -700HY; the reading of 35.2% was higher than -699HU. Conclusion: Respiratory status significantly affects the quantitative ace- ssment of pulmonary parenchyma; in order to determine, during quantitative HRCT, the parameters of a pathologic condition, lung parenchyma of differing respiratory status must be evaluated.