Autotransplants of blood progenitor cells are increasingly used in persons with cancer, sometimes added to bone marrow cells but increasingly in their stead. Clearly, transplants of blood progenitor cells accelerate hematopoietic recovery after high-dose therapy. However, because some residual recipient-derived hematopoiesis typically persist even after the most intensive therapy, it is not certain that long-term hematopoiesis is from the blood progenitor cell autograft. However, this issue may be unimportant since the immediate goal is short-term recovery of bone marrow function regardless of which cells are responsible for long-term recovery. This issue is, however, of considerable import were more intensive treatment to be used or where blood progenitor cells were to be used for allografts. There are some reasons to think that transplants of blood-derived cells might have a lower likelihood of returning cancer cells to the recipient, at least in some lymphomas and solid tumors, than an autotransplant of bone marrow cells. This notion is as yet unproven and may be important only when and if more effective anti-cancer pretransplant regimens are developed. The potential role of transplants of blood progenitor cells depends on how useful autotransplants prove. Whether use of blood progenitor cells rather than bone marrow cells offers any advantage requires considerable additional data and controlled trials.