Therapeutic angiogenesis using angiogenic growth factors is expected to be a new treatment for patients with critical limb ischemia (CLI). Because hepatocyte growth factor (HGF) has potent angiogenic activity, we investigated the safety and efficiency of HGF plasmid DNA in patients with CLI as a prospective open-labeled clinical trial. Intramuscular injection of naked HGF plasmid DNA was performed in ischemic limbs of 6 CLI patients with arteriosclerosis obliterans (n=3) or Buerger disease (n=3) graded as Fontaine III or IV. The primary end points were safety and improvement of ischemic symptoms at 12 weeks after transfection. Severe complications and adverse effects caused by gene transfer were not detected in any patients. Of particular importance, no apparent edema was observed in any patient throughout the trial. In addition, serum HGF concentration was not changed throughout the therapy period in all patients. In contrast, a reduction of pain scale of more than 1 cm in visual analog pain scale was observed in 5 of 6 patients. Increase in ankle pressure index more than 0.1 was observed in 5 of 5 patients. The long diameter of 8 of 11 ischemic ulcers in 4 patients was reduced >25%. Intramuscular injection of naked HGF plasmid is safe, feasible, and can achieve successful improvement of ischemic limbs. Although the present data are conducted to demonstrate the safety as phase I/early phase IIa, the initial clinical outcome with HGF gene transfer seems to indicate usefulness as sole therapy for CLI.