Multiple myeloma (MM) remains an incurable disease by conventional therapy. MM tumor cells evade the immune system and can induce immunosuppression by producing immunomodifying agents such as TGF-β, FasL, vascular endothelial growth factor and Muc-1. In the present study, we show that bone marrow cells from a patient suffering from MM IgG/k type, stage IIIA, when cultured, expressed granzyme B and perforin, normally expressed exlusively by cytotoxic T cells (CTLs) and natural killer (NK) cells. In addition, phenotypic analysis revealed that the cultured cells were activated antigen-presenting cells with NK targeting capacity. We propose that expression of these cytolytic enzymes may constitute an additional adoptive mechanism by the tumor cells to actively destroy the host immune effector cells.