The use of peripheral blood stem cells (PBSC) as a source of hematopoietic stem cells is steadily increasing and has nearly supplanted bone marrow transplantation. The present article reviews mobilization of PBSC as well as the side effects. Under steady state conditions less than 0.05% of the white blood cells (WBC) are CD34+ cells. Chemotherapy results in a 5-15-fold increase of PBSC. Combining chemotherapy and growth factors increases CD34+ cells up to 6% of WBC. In the allogeneic setting, granulocyte-colony stimulating factor (G-CSF) is used alone for PBSC mobilization. Several factors affect the mobilization of PBSC: age, gender, type of growth factor, dose of the growth factor and in the autologous setting, the patient's diagnosis, chemotherapy regimen and number of previous chemotherapy cycles or radiation. Muscle and bone pain are frequent adverse events in allogeneic stem cell mobilization but are usually tolerated with the use of analgesics. Spleen enlargement followed by rupture is a serious complication in allogeneic donors. Large volume apheresis (LVL) with a processed volume of more than 4-fold of the patient's blood volume can be used to increase the CD34+ yield in patients with low CD34+ pre-counts, resulting in higher yields of CD34+ cells for transplantation. Processing of more blood in LVL is achieved by an increase of the blood flow rate and an altered anticoagulation regimen with the occurrence of more citrate reactions.