PURPOSE: Dynamic liver scan with spiral CT during a single breath hold was performed for To determing the optimal timing of scanning and the degree of the enhancement of liver and vessel. MATERIALS AND METHODS: Liver spiral CT was performed on 143 patients and dynamic sequence scan on 2 normal volunteers. After baseline spiral CT without contrast enhancement, spiral CT was performed after administration of a bolus of 100 ml of nonionic contrast material intravenously with mechanical power injector at the constant injection rate of 2 ml/sec. Cephalocaudal scanning was started 45 seconds after the beginning of injection. In the majority of cases we employed 16-24 continuous scanning with table feed of 10 mm, slice thickness of 10 mm, and reconstructed in 5 or 10 mm section increments. We measured degree of enhancement of aorta, IVC, and liver parenchyma in all images. RESULTS: We have achieved bolus phase at all images from the following measured date; 170-250 H. U at aorta, 110-150 H. U at IVC, 80-125 H. U at liver parenchyma, 100-130 H. U at spleen, which shown contrast difference between aorta and IVC at least 45 H. U. At the dynamic sequence scan, aortic and vascular CT atternuation reaches a peak at 55-60sec and peak hepatic enhancement occurred at 70-75 sec with relative plateau achieve at 45 sec. Spiral CT also showed elimination of variation in diaphragmatic excursion. CONCLUSION: We could get the disirable phase imaging at overall examination from the dynamic liver scan around 45-60 seconds after injection of contrast media.