To assess the effect of partial portal arterialization on the remaining liver after usually lethal extended hepatectomy, 30 mongrel dogs underwent 84% partial hepatectomy and were divided into three groups as follows: group 1, 84% partial hepatectomy (n = 10); group 2, 84% partial hepatectomy and splenectomy (n = 10); group 3, 84% partial hepatectomy and splenectomy and splenic artery-vein (A-V) shunt (n = 10). Another five dogs were pre-operatively killed normal controls. Portal vein flow (PVF) decreased to about 60% in groups 1 and 2, but PVF in group 3 was maintained at the pre-operative level. Oxygen saturation of portal vein blood increased markedly, to between 83% (group 1) and 88% (group 3). Portal vein pressure (PVP) increased in groups 1 and 2 by 1.6 to 1.7 times the pre-operative value, but no significant difference in PVP, serum aspartate aminotransferase (AST) and arterial ketone body ratio was found between the three groups. Plasma endotoxin levels after 84% partial hepatectomy were significantly lower in group 3 than in groups 1 and 2. Both of hepatocellular and secretory protein synthesis were enhanced in group 3 compared with the other two groups. These results suggest that partial portal arterialization using a splenic A-V shunt might bring about a beneficial effect on remaining liver function after extended hepatectomy.