The use of G-CSF for mobilization of stem and progenitor cells is a widely used clinical technique for both autologous and allogeneic transplantation which has proved both safe and effective. Bone and muscle pain, headache and fatigue are the most common complications which are typically managed with acetaminophen and rarely require discontinuation of G-CSF. Transient elevations in alkaline phosphatase and LDH are common. Follow-up studies have shown prolonged, mild neutropenia, lymphopenia and thrombocytopenia following G-CSF administration and apheresis. Splenic enlargement has been shown by non-invasive measurements and four cases of splenic rupture in normal individuals have been described. A reduction in arterial pO2 associated with a decrease in the O2 saturation from 98 to 96% has been reported. Transient thrombophilia has been inferred based on changes in blood coagulation parameters.