Hematopoietic growth factors can be used for the mobilization of peripheral blood stem cells that have the proliferative capacity to restore long-term hematopoiesis after myeloablative therapy. An association between specific cytokines and the composition of the blood-derived progenitor cells has not yet emerged. It appears that yield and composition of PBSC are influenced far more by the individual than by the use of specific growth factors. Our future studies will focus on how many and what kind of stem cells are needed for high-dose regimens with different myelotoxicity. In parallel, autografts will be assessed for contaminating tumor cells, if disease- or clone-specific markers are available. This approach may then provide the rationale for the increasing use of PBSC for autografting.