EBV-induced lymphoproliferative disease (EBV-LPD) is a disorder most commonly associated with the immunocompromise that follows allogeneic organ transplantation. In patients receiving T cell-depleted bone marrow from HLA-mismatched or HLA-matched unrelated donors, the incidence of EBV-LPD is particularly high, ranging from 5 to 30%. Administration of EBV-specific cytotoxic T lymphocytes may be one means of preventing and treating this disease. We now describe a method that allows the routine and timely preparation of large numbers of such cells to allow their safe administration to bone marrow transplant recipients. We also describe how these cells may be genetically marked before infusion, to determine their fate and disposition in vivo.