Intra-arterial digital subtraction angiography using CO2 (CO2-IA-DSA) is effective for detecting arteriovenous and arterioportal shunts in the liver. We carried out CO2-IA-DSA in addition to selective arteriography using a iodinated contrast medium in 31 patients with unresectable hepatocellular carcinoma (HCC). As a result, CO2-IA-DSA detected an AV shunt in 4/31 patients and an AP shunt in 16/31 patients for a total of 20 cases of shunt, whereas conventional hepatic IA-DSA detected only AP (AV shunt) shunts in 3/31 patients. For HCC without any shunt, Gelfoam embolization was carried out after injection of Lipiodol and Farmorubicin (FARM). In patients with an AP shunt, injection of Lipiodol and FARM was performed after the shunt had been embolized with Gelfoam. In patients with an AV shunt, Lipiodol and FARM were injected after the shunt had been embolized with a metallic coil. In conclusion, detection of shunts by CO2-IA-DSA is useful for determining the optimal approach for transcatheter arterial injection.