It has been demonstrated that the injection of naked DNA expressing vascular endothelial growth factor 165(VEGFl165) to the affected area can provide significant therapeutic effects on peripherol artery occlusive diseases. Success with this type of gene therapy highly depends on the quality of the vector delivering the therapeutic gene, especially in terms of the level and duration of gene expression in the localized area. We have recently developed a vector expressing VEGF165(pCK-VEGF) for the treatment of peripheral artery occulsive diseases and demonstrated high level expression of VEGF165 in mouse skeletal muscle. This study was designed to assess the acute toxicity of intramuscularly injected pCK-VEGF in BALB/c mice and Sprague-Dawely rats. There was no evidence of any changes in clinical signs, body weights, or gross pathological signs. We estimate LD50 values of pCK-VEGF higher than 50mg/kg in mice and 20 mg/kg in rats by intramuscular injection.