Reactivation of hepatitis B virus in patients receiving chemotherapy for non-Hodgkin's lymphoma (NHL) may give rise to hepatitis, hepatic failure and death, and prevent further chemotherapy. We report four patients with NHL in whom hepatitis flare-up was observed after two (three patients) and six (one patient) cycles of chemotherapy. After spontaneous recovery, they were treated with Lamivudine (100 mg/day), which enabled completion of chemotherapy without further hepatitis B reactivation. In one patient, high-dose chemotherapy and autologous stem cell transplantation was also performed. These data suggest a possible role for Lamivudine in preventing hepatitis B reactivation during chemotherapy administration to chronic carriers of the hepatitis B virus. Moreover, it enabled the completion of both standard and high-dose chemotherapy in patients with previous hepatitis B reactivation.