BACKGROUND: Clinical and Radiographic studies to differentiate benign from malignant pulmonary nodules have previously focused on clinical status and the morphologic and the computed tomographic attenuation characteristics of the lung nodules. Distinctive differences in the vascularity and pathophysiology of malignant versus benign pulmonary nodules were identified. We evaluated the diagnostic method for differentiating malignant from benign solitary pulmonary nodule by contrast enhancement on the spiral CT. METHOD: Sixteen patients with solitary pulmonary nodule were examined(Tuberculoma 8, primary lung cancer 8). Serial thin section on the spiral CT was performed before and after(45second, 2min, 5min) the onset of the injection of 100mL of nonionic contrast material(2mL/sec). RESULTS: There was no difference in size of nodule and pre-contrast CT number (Hounsfield unit) between benign and malignant nodules. At forty-five second after the onset of the injection, malignant neoplasms(19.6+/-7.9 HU) enhanced significantly more than tuberculomas(4.9+/-9.4 HU, p=0.008). At 2 minute and 5 minute after, malignant neoplasms(34.0+/-19.2HU, 340+/-15.4HU) enhanced significantly more than tuberculomas (6.7+/-9.7HU, p=0.007 and 7.7+/-11.5HU, p=0.011). On cut-off value 20HU(contrast enhancement) 2 minute after the injection of contrast media, sensitivity was 87% and specificity was 87%. No correlation between the contrast enhancement and size of the nodules was observed. CONCLUSION: Studies with the use of an intravenously administered noniodinated contrast medium in examining the enhancement properties of lung nodules was performed. The contrast enhancement was useful in differential diagnosis of solitary pulmonary nodules.