There is increasing interest in the use of allogeneic blood and marrow transplants for chronic lymphocytic leukemia (CLL) and lymphomas. Numerous studies indicate efficacy in patients with advanced disease and demonstrate existence of a potent graft-versus-malignancy effect against these disorders. Allogeneic transplantation is most effective in CLL and low-grade lymphomas, but precise indications and timing of allogeneic transplants in these indolent disorders are not well defined. Allotransplantation is an effective, potentially curative approach, albeit with substantial risks; it is indicated in selected categories of patients. Allogeneic transplants are also promising for mantle cell lymphoma. In large-cell lymphoma, relapses are reduced in allogeneic compared with autologous transplants, but the benefit of allotransplantation has been offset by increased risk of treatment-related complications, and its indications are controversial. A promising new strategy is the use of less toxic, nonmyeloablative preparative regimens to achieve engraftment and allow development of graft-versusmalignancy effects that can produce durable remission in selected categories of lymphoid malignancies.