PURPOSE: To determine the potential of spiral CT as a functional imaging modality of the lung asid from its proven value in morphological depiction. MATERIALS AND METHODS: Spiral CT scan was performed in ten normal female and nine normal male adults (mean age: 39, height: 163cm, weight: 62kg) after single full breath-holding. Three dimensional lung images were reconstructed (minimal threshold value: -1,000HU, maximal threshold values: -150,-250, -350, -450HU) to obtain total lung volume(TLV) on a histogram. Total lung volume measured by spiral CT was compared with TLV obtained by spirometry. RESULTS: Mean TLV measured by spirometry was 5.62 Land TLV measured by CT at maximal threshold values of -150, -250, -350, and -450HU was 6.63, 5.33, 5.15, and 4.98 L, respectively. Mean absolute differences between the modalities of 0.17L(3%), 0.32L(5.6%), 0.48L(8.5%), 0.65L(11.5) were statistically significant(p<0.001). Linear regression coefficients between the modalities were 0.99, 0.97, 0.95,and 0.94 and no statistically significant differences in accuracy of threshold levels in the estimation of lung volume(r=0.99, standard error=0.034L in all) were seen. CONCLUSION: TLV measured by spiral CT closely approximated that measured by spirometry. Spiral CT may be useful as a means of evaluating lung function.