Reinfection with hepatitis B virus after orthotopic liver transplantation is nearly universal in patients who have not received posttransplant immunoprophylaxis. Recurrence almost invariably leads to chronic liver disease. Interferon has been used both prophylactically and therapeutically but has not been effective. We treated 2 liver transplant patients with recurrent hepatitis B virus (HBV) infection (serum hepatitis B surface antigen [HBsAg] and HBV DNA positive on polymerase chain reaction, and positive liver biopsy result) with interferon, 3 to 6 MU three times weekly for 6 to 22 months. A full response to therapy was manifested in both patients by normalized serum alanine aminotransferase levels and the loss of serum HBsAg and HBV DNA. The effectiveness of interferon in our patients may have been related to coinfection with hepatitis D virus in the first case and the high interferon dose (6 MU, three times weekly) and long treatment period (22 months) in the second. No episodes of rejection were noted during therapy. We conclude that interferon can induce a complete response in liver transplant patients with recurrent HBV infection. Future studies should investigate the use of interferon therapy at higher doses and/or for longer periods.