100 years ago, hematopoietic stem cells were postulated as blood lymphocyte-like cells. Within the last 20 years, the frequency of autologous and allogeneic transplantation of hematopoietic stem cells has increased. Hematopoietic growth factors allow the stem cells' mobilization from the bone marrow into the peripheral blood. Quantification of these hematopoietic stem cells by means of flow cytometry can be achieved within hours. A minimum quantity of 2.0 x 10(6) CD34-positive blood stem cells per kg body weight allows hematopoietic reconstitution within 14 days after infusion of the transplant. High-dose therapy followed by the transplantation of autologous blood stem cell transplantation is an established therapy for relapsed high-grade lymphoma and multiple myeloma. Especially in cases of subgroups of acute myeloid leukemia, myelodysplastic syndrome and myeloproliferative syndromes, myeloablative high-dose therapy followed by the transplantation of allogeneic stem cells leads to a better prognosis. Reduced conditioning before an allogeneic transplantation decreases early lethality. The combination of myeloablative high dose therapy followed by autologous hematopoietic stem cell transplantation and allogeneic stem cell transplantation will lead to maximum tumor reduction and development of a graft-versus-leukemia reaction with reduced toxicity. Hematopoietic stem cell transplantation is to be carried out in studies.