Recombinant G-CSF has been given to over 150 normal donors for the collection of allogeneic or syngeneic peripheral blood stem cells (PBSC). G-CSF was found to be well-tolerated with mild-moderate bone pain, edema and mild thrombocytopenia being the observed side effects. To date, approximately 90 unmodified primary PBSC transplants from HLA-identical related donors have been performed with engraftment that is, in general, considerably more rapid than marrow. Acute graft-versus-host-disease (GVHD), grades II-IV occurred in 47% of patients and grades III-IV in 17%. Despite the infusion of one to two logs more T cells, these results are not remarkably different than would be expected with marrow transplantation. There have also been successful reports of using G-CSF mobilized allogeneic PBSC following second transplants for graft rejection or relapse. Allogeneic PBSC have been infused without reconditioning for correction of graft failure and unmodified or CD34 selected PBSC have also been given with marrow to augment the dose of hematopoietic cells. Further studies are needed to define the role of allogeneic PBSC for transplantation, refine PBSC mobilization and collection techniques and to evaluate the long-term effects of cytokines in normal donors.