Due to the limited supply of livers for transplantation and acute situations in which an orthotopic liver transplantation (OLT) is needed, nonidentical ABO blood group OLTs are performed. One of the risks of transplanting an O liver into an A/B/AB recipient is the development of hemolysis. We managed 2 cases of ABO-compatible but nonidentical OLTs. Both recipients suffered from Wilson's disease (blood group B+ ) and received a blood group O+ donor liver. One of them was a 39.5 kg, 12 year-old-girl and the other was an 81 kg, 21 year-old-woman. The average duration of anesthesia was about 12 hr 30 min and the anhepatic times were 51 min and 57 min, respectively. During and after the operation, we used the recipients' type packed red cells and fresh frozen plasma. Hemodynamic values, serum electrolytes and blood coagulation were relatively well maintained throughout the operation. A mild decrease in hematocrit was observed 10 and 7 days after operation, respectively. However, there was no evidence of hemolysis, clinically.