Therefore, the primary intent of this protocol is to provide a mechanism for mobilizing, collecting, storing, and analyzing G-CSF mobilized apheresis samples from healthy volunteers. Cells will be used to develop a method of processing the cells that are collected after stimulation with G-CSF, by removing the lymphocytes, which can mediate GVHD while retaining the stem cells which are necessary for hematopoietic reconstitution. At the same time we will study whether G-CSF administration has an effect on the lymphocyte, function which may influence the immune reactions occurring in allogeneic bone marrow transplantation. Furthermore the CD34+ cells collected will be a valuable resource for experimental studies of lymphocyte-stem cell interactions in our laboratory.