Background: Beneficial effects of bone marrow stem cell transplantation in patients with MI brought the need of noninvasive stem cell mobilization. Safety and feasibility of G-CSF induced stem cell mobilization and mobilized cell infusion is unknown. We tested the clinical feasibility and effects of G-CSF induced mobilization and intracoronary infusion in patients with MI. Methods: We randomly allocated 22 patients (56 짹 11years old, LVEF =50 짹 12%) to onet of three group: 1) G-CSF group: G-CSF induced mobilization(n= 10, 6 AMI patients), 2) Infusion group: intra-coronary infusion of G-CSF mobilized cells(n = 10, 4 AMI patients), 3) Non-mobilization group(n=2, 2 AMI patients). G-CSF with 10ug/kg/day for 4.2 짹 0.7 days were administrated to G-CSF and infusion group. And then all groups underwent percutaneous coronary intervention(PCI) for culprit lesion. MIBI SPECT and PET were performed before PCI and treadmill test and dobutamine stress echo were performed after PCI. Follow up coronary angiography and noninvasive study were performed 6months later. Results: Patients in each study group showed no significant differences in baseline characteristics. No adverse reaction was observed except mild headache(3patients) with G-CSF administration. Patients in infusion group underwent apheresis before PCI and 1.5 짹 0.5 x 10⁹ leukocytes(7.6 짹 2.9 x 10⁷ CD 34+ cells) were infused after PCI without complication. Elevation of CK-MB after PCI were comparable among study groups(Before and 12hours after PCI, Infusion group: 2.2 짹 2.2 vs. G-CSF group: 0.3 짹 3.1 vs. Non-mobilization group: 1.5 짹 0.7U/L, p=0.34). Symptom and ECG had not changed after PCI. No reflow phenomenon was not observed and coronary flow reserve did not worsened with cell infusion(before and 10minutes after infusion: 1.7 짹 0.4 vs. 1.7 짹 0.5: P=0.75). Three symptomatic restenosis(one from cell infusion group and two from G-CSF group) were observed during mean 4 짹 1month clinical follow up. Conclusions: G-CSF is a feasible and safe stem cell mobilizer in MI. Apheresis and whole leukocyte infusion after G-CSF mobilization is a practical method of stem cell transplantation.