As a surgical method for the treatment of unresectable hepatocellular carcinoma (HCC), we developed a new therapy which consists of intermittent hepatic arterial occlusion (IHAO) during infusion chemotherapy by the use of double lumen balloon catheter inserted into the hepatic artery. This therapy was performed in 23 cases with unresectable HCC. Antineoplastic effects judged by Karnofsky's criteria were I-B in 19,I-A in three and 0-0 in one case. It was proved that the anticancer drug remained for a longer period at higher concentrations in the liver during IHAO. With the advance of gradual induction of thrombosis from peripheral hepatic artery by frequent HAO, liver dysfunction, growth of collateral vessels and repatency after induction of thrombosis could be suppressed. We conclude that this new therapy is a safe and more effective procedure for unresectable HCC and will have a wide application.