The author has developed the intrahepatic portal vein embolization for the treatment of liver cancers. The purposes of this new method are 1) extension of indications for surgery by causing compensatory hypertrophy of non-embolized lobe, 2) prevention of dissemination of the tumor cells via the portal vein, 3) causing complete ischemic necrosis of the tumor together with arterial embolization, and 4) blockade of centripetal extension of tumor thrombus. The feasibility and safety of this method were studied experimentally. Three kings of materials were prepared for embolization of the portal vein; a Lipiodol-thrombin mixture (Lp-T), a Lipiodol-fibrin adhesive mixture (Lp-F), and a mixture of Lipiodol with isobutyl-2-cyanoacrylate (Lp-IBC). The portal vein was embolized in 31 dogs, 6 with Lp-T, 14 with Lp-F, and 11 with Lp-IBC. Lp-F was used 30 to 90 seconds after preparation, which had been found to be best in an in vitro study. Lp-T and Lp-IBC could be used at any time after preparation. Embolization was done safely and reliably, except in two cases of Lp-F, by use of a balloon catheter for Lp-T or Lp-F and a coaxial catheter for Lp-IBC. Follow-up portography showed recanalization in one week in the dogs embolized with Lp-T. The obstruction was maintained for two to four weeks in the dogs embolized with Lp-F, and for four weeks in all dogs embolized with Lp-IBC. Damage in the liver was slight both macroscopically and histologically. Changes in liver function and elevation of the pressure of the portal vein were transient. The author concluded that the intrahepatic portal vein embolization was both feasible and safe when the materials tested were used, and could be an effective method for liver cancers. In clinical cases, Lp-T would be suitable for short-term occlusion, Lp-F for a moderate term, and Lp-IBC for long-term. The material should be selected with regard to the purpose.