Auxiliary partial hepatic allografts were performed between ten pairs of closely bred beagles typed for certain leukocyte and erythrocyte specificities. All totally leukocyte-incompatible recipients rejected the grafts in less than 11 days. The grafts survived with little evidence of rejection in two compatible littermate recipients until termination at 150 days. These grafts maintained virtually normal levels of total bilirubin and serum glutamic oxaloacetic transaminase following division of the host's common bile duct; the serum alkaline phosphatase level was slightly elevated. The closely-bred histocompatible beagle is a suitable model for further testing the utility of the auxiliary liver transplant.