Purpose : To assess the value of dynamic fast infusion of contrast material in the detection and diagnosis of hepatocellular carcinoma(HCC) with spiral CT. Materials and Methdos : Two-phase dynamic spiral CT was performed in59 patients with 104 HCCs. 150ml of nonionic contrast material was injected with an automatic injector at the rate of 5 ml/sec. Two-phase images were obtained at 20-45 sec(arterial dominant phase) and 2-5 min(equilibrium phase)after the initiation of bolus injection of contrast material. The tumors were divided into three groups(<3cm, 3-5cm, and>5cm) according to the size and the enhancement patterns on two-phase images were compared. Results : In the arterial phase, HCCs showed total or partial hyperattenuation in 79% of cases(82/104), isoattenuation in 12%, and hypoattenuation in 9%. In the equilibrium phase, HCCs showed hypoattenuation in 86%(89/104) and isoattenuationin 14%. The most common and characteristic enhancement patterns of HCCs were hyperattenuation in the arterial phase and hypoattenuataion in the equilibrium phase ; in the latter, capsules were demonstrated in 45% of cases. Invasions of the portal and/or hepatic vein were demonstrated in 34% of cases. Conclusion : Dynamic fast infusion(5ml/sec) of contrast material(150ml) is useful in the detection and diagnosis of HCCs with spiral CT.