Partial liver transplantation (PLTR) was studied experimentally, using 60 monkeys (20 recipients, 20 donors, 20 blood donors). The left lobe of the donors was transplanted orthotopically, using a veno-venous bypass catheter that was inserted in the portal vein and the other side passed through the hepatic portion of the inferior vena cava. The donor survival rate at 1 week was 70%. Seven recipients survived for more than 58 hours (58, 60, 64, 68, 72, 110, and 252 hours), and 13 died within 48 hours of surgery because of postoperative complications. Clinical living related liver transplantation (LRLT) was performed between June 1990 and March 1992 on six patients with biliary atresia and on one with liver cirrhosis and hepatocellular carcinoma. In all, the father's left lobe was transplanted orthotopically. Cyclosporine, azathioprine, and methyl prednisolone were administered. In addition, FK-506 was given to two patients in whom rejection was observed; one died 37 days after surgery because of acute rejection followed by systemic cytomegalovirus infection. The other six patients have survived for 8 to 29 months since transplantation. All six have been discharged from the hospital and are enjoying normal daily life. The postoperative course of all donors was uneventful. They were discharged 2 weeks after the operation and returned to their jobs in 2 months. The authors conclude that PLTR from a living donor is a promising therapeutic alternative to liver transplantation from a cadaver.