Background: This study was undertaken to evaluate the hypothesis that treatment with granulocyte colony-stimu-lating factor(G-CSF) to mobilize bone marrow cells(BMCs) is feasible and safe and promotes neovascularization and myocardial function in patients with acute myocardial infarction. Methods: Fourteen patients in the treatment group and 9 patients in the control group were enrolled in this prospective, nonrandomized, open-label study. Forty-eight hours after successful recanalization and stent implantation, the patients of the treatment group received 10 μg/kg body weight per day G-CSF subcutaneously for mean treatment duration of 7.0±1.0 days. Nine patients fulfilled the entry criteria but refused participation and served therefore as control group. In both groups, regional wall motion and perfusion was evaluated with electrocardiogram-gated sestamibi single-photon emission computed tomography imaging and ejection fraction with radionuclidventriculography before discharge and after 3 months. Results: No severe side effects of G-CSF treatment were observed. There was a significant improvement of the regional wall motion and perfusion within the treatment group(P< .0001) and between the treatment and control group(P< .05 and P< .01, respectively). Ejection fraction in the treatment group increased from 0.40±0.11 to 0.48±0.13(P< .01), whereas in the control group, ejection fraction increased from 0.40±0.13 to 0.43±0.13(P=.049). A control angiography of the treatment group after 12.4±6.6 months showed an in-stent restenosis in 1 patient. Conclusion: In patients with acute myocardial infarction, treatment with G-CSF to mobilize BMCs is feasible and safe and seems to be effective under clinical conditions. The therapeutic effect might be attributed to BMC-associated promotion of myocardial regeneration and neovasculariza-tion. Background: This study was undertaken to evaluate the hypothesis that treatment with granulocyte colony-stimu-lating factor (G-CSF) to mobilize bone marrow cells (BMCs) is feasible and safe and promotes neovascularization and myocardial function in patients with acute myocardial infarction. Methods: Fourteen patients in the treatment group and 9 patients in the control group were enrolled in this prospective, nonrandomized, open-label study. Forty-eight hours after successful recanalization and stent implantation, the patients of the treatment group received 10 μg / kg Body weight per day G-CSF subcutaneously for mean treatment duration of 7.0 ± 1.0 days. Nine patients fulfilled the entry criteria but refused participation and served therefore as control group. In both groups, regional wall motion and perfusion was evaluated with electrocardiogram-gated sestamibi single-photon emission computed tomography imaging and ejection fraction with radionuclidventriculography before discharge and a There was a significant improvement of the regional wall motion and perfusion within the treatment group (P <.0001) and between the treatment and control group (P <.0001) .05 and P <.01, respectively). Ejection fraction in the treatment group increased from 0.40 ± 0.11 to 0.48 ± 0.13 (P <.01), while in the control group, ejection fraction increased from 0.40 ± 0.13 to 0.43 ± 0.13 (P = .049). A control angiography of the treatment group after 12.4 ± 6.6 months showed an in-stent restenosis in 1 patient. Conclusion: In patients with acute myocardial infarction, treatment with G-CSF to mobilize BMCs are feasible and safe and seems to be effective under clinical conditions. The therapeutic effect might be attributed to BMC-associated promotion of myocardial regeneration and neovasculariza- tion.