The development of Epstein-Barr virus-associated posttransplantation lymphoproliferative disease correlates with increased viral burden in lymphocytes. Patterns of viral gene expression in tumors are complex and heterogenous. Conventional chemotherapy for postransplantation lymphoproliferative disease is sometimes associated with long-term disease-free survival. A promising new approach involves adoptive cellular immunotherapy with donor lymphocytes or T-cell lines. Allogeneic bone marrow transplantation has been successful in patients with an inherited lack of immune response to Epstein-Barr virus.