Reactivation of hepatitis B infection (HBV) is known to occur in liver graft recipients and in chronic carriers of the surface antigen of HBV who receive immunosuppressive therapy. The use of hepatitis B immune globulin alone or in combination with antiviral agents such as lamivudine, adefovir, tenofovir, entecavir, famciclovir, ganciclovir, as prophylaxis in HBV liver transplants, has been well documented. In terms of HBV positive carriers undergoing cytotoxic chemotherapy, the preemptive use of nucleoside or nucleotide analogues seems to be effective. Monotherapy or combination of antiviral drugs, as well as the optimal duration of HBV prophylaxis, is to be determined.