The effect of portal arterialization was examined in 20 heterotopic auxiliary rat livers. Portal blood was supplied from recipient iliac artery (0.58 mm in diameter) connected to the donor portal vein using the cuff technique. Portal hypertension caused by arterial blood pressure resulted in the immediate operative death by bleeding in four of the rats (20%) from the spontaneous rupture of the graft capsule. Severe graft congestion was noticed at autopsy 3-14 days after transplantation in 13 rats. Massive portal and sinusoidal congestion and focal hemorrhagic necrosis were confirmed by pathological examination. The results of our study demonstrate that the portal arterialization used in the auxiliary rat liver transplantation would not be applicable unless the optimal hemodynamic condition is warranted.