Recombinant G-CSF has been given to over 150 normal donors for the collection of allogeneic or syngeneic peripheral blood stem cells (PBSCs). 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 100 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 44% of patients and grades III-IV in 16%. From a small number of evaluable patients surviving for more than 100 days, it appears the incidence of chronic GVHD is approximately 50%. Despite the infusion of one to two logs more T cells, these results are not remarkably different than would be expected with marrow transplantation. Further studies are needed to define the role of allogeneic PBSCs for transplantation, to refine PBSC mobilization and collection techniques, and to evaluate the long-term effects of cytokines in normal donors.