We evaluated the usefulness of preoperative portal vein embolization (PVE) in rats for increasing the safety of liver resection. During PVE, portal vein branches that perfused the central and left lobes of the liver were embolized. Liver weight, the elimination of indocyanine green, and the number of Kupffer cells were examined 7 days after PVE and in intact rats. Then we examined rats that had undergone PVE (PVE group), rats in which the embolized part of the liver was resected 7 days after PVE (PVE-Hx group), rats without PVE in which the same lobes of the liver were resected (Hx group), and rats that had undergone a sham operation (sham-operation group) for liver weight, the mitotic index of the hepatocytes, serum alanine aminotransferase activity, total bilirubin, and antithrombin III activity. Some rats in the four groups received an intravenous injection of 0.5 or 2.5 mg/kg endotoxin 48 hr after the operation (the second operation, if done), and the 24-hr survival rate was calculated. Some rats given 0.5 mg/kg endotoxin were killed 6 hr after the injection, and the extent of liver injury was examined biochemically and histologically. Seven days after PVE, the nonembolized part of the liver was about twice the weight of the corresponding lobes in the intact rats, the density of Kupffer cells was doubled, and the hepatic function per unit weight was about the same as that in these controls. Hepatic dysfunction and the endotoxin-induced liver injury were significantly slighter in the PVE and PVE-Hx groups than in the Hx group. Preoperative PVE could make hepatectomy safer.