Peripheral blood progenitor cells (PBPCs) are an effective source of hematopoietic stem cells for autologous or allogeneic transplantation. Progenitors must be mobilized into the circulation to allow efficient collection. Some promising mobilizing regimens include the use of stem cell factor and growth factors such as interleukin-3, granulocyte colony-stimulating factor, and granulocyte-macrophage colony-stimulating factor. Transplantation of PBPCs has several advantages over bone marrow transplantation: larger numbers of progenitors can be collected, general anesthesia and multiple bone marrow aspirations can be avoided, and hematologic recovery appears to be more rapid and predictable with PBPCs. The disadvantages of using PBPCs for transplantation include the costs of multiple aphereses and purging procedures, the requirement for a mobilizing regimen, and the necessity for vascular access. Several uncertainties remain regarding the transplantation of PBPCs, including the optimal dose and composition of cells for transplantation.