Epstein-Barr virus (EBV) infection can induce uncontrolled lymphocyte B proliferation in immunosuppressed transplant patients. Monitoring circulating EBV-infected lymphocytes can help in identifying patients at risk of posttransplant lymphoproliferative disease (PTLD). Circulating EBV genome levels were determined in 54 liver transplant pediatric recipients. Ten patients had more than 500 EBV genome/10(5) peripheral blood lymphocytes (PBL) and exhibited clinical manifestations of EBV infection; three developed PTLD. To treat EBV infection, the level of immunosuppression was reduced and acute rejection developed in 4 patients. Three were treated with steroid and one had to be switched from cyclosporine to tacrolimus. Treatment of acute rejection was associated with increases in circulating EBV genome. None of the patients with less than 500 EBV genome/10(5) PBL developed PTLD or EBV infection. Monitoring of EBV DNA is useful in the management of EBV infection and PTLD following pediatric liver transplantation. EBV infection should be treated in ways which do not expose patients to the risk of rejection.