BACKGROUND: The safety and efficacy of autologous bone marrow-derived mononuclear cell (BM-MNC) transplantation in the treatment of lower limb ischemia is becoming established, although common treatment protocols are not yet agreed upon. We hypothesized that bone marrow mobilization with granulocyte colony-stimulating factor (G-CSF) improves the safety and effectiveness of cellular therapy. METHODS: Forty-four patients were randomly assigned to receive two injections of G-CSF (300 mu g) prior to BM-MNC transplantation. BM-MNC were harvested from all patients and injected as equal aliquots of at least 10(8) cells into the ischemic leg muscles below the lowest patent artery. RESULTS: After 3 months, patients receiving G-CSF reported increased subjective relief of symptoms and showed increased transcutaneous oxygen tension (TcPO2). After 6 months, patients showed greater improvement in TcPO2, ankle-brachial index, and angiographic score compared to control patients. There were no increased numbers of side effects in patients receiving G-CSF. CONCLUSIONS: G-CSF is safe and effective to mobilize BM-MNC and may allow reduced volume of aspirated bone marrow, potentially reducing procedural complications. G-CSF should be considered for use in patients that are candidates for angiogenic therapy. G-CSF may increase the number of patients that are candidates for therapeutic angiogenesis.