Bone marrow transplantation gradually expanded as a treatment modality for various malignant and non malignant disease conditions. Since the discoveries of the potential of Peripheral Blood Progenitor Cells (PBPC) in the hematopoietic reconstitution mid 1980s and early 1990s PBPC gradually replaced bone marrow as the preferred source of stem cells. The introduction of hematopoietic cytokines that can mobilize large number of progenitors into circulation accelerated PBPC usage. Technological advancements in the apheresis instrumentation greatly helped in the conversion from marrow to PBPC. PBPC collection is less painful, less expensive and transplant with PBPC results in faster hematological recovery than with marrow. Almost all of the autologous transplants are currently performed with PBPC and a similar trend is seen with the allogeneic transplants. The progenitor cell mobilization regimen for autologous patients can be cytokines alone or cytokines combined with chemotherapy. In the majority of the patients the required minimal cell dose of 2.5-5.0 x 10(6)/kg CD34+ cells can be collected in one or two apheresis collections. A few of autologous transplant patients who mobilize poorly require several collections. Allogeneic donors are generally mobilized with daily subcutaneous injections of G-CSF 10 microg/kg for 5 days. The PBPC are collected in one or two apheresis procedures. The side effects of G-CSF are generally mild to moderate; however rare serious reactions including rupture of the spleen have been reported. The collection of PBPC in pediatric patients poses additional challenges yet an adequate dose of cells can be collected with the available apheresis instrumentation. The apheresis collection procedures are safe with no serious adverse consequences. Future scientific advancements may expand the use of PBPC for other clinical application in addition to the current use for hematological reconstitution.