To verify that preservation of vascular DDAH activity and its protein expression being involved in the mechanism underlying PDTC protection against diabetes-induced impaired vasodilation, ex vivo DDAH2 gene transferring to isolated aortic rings of diabetic rats was performed to compare its effect with that of PDTC treatment on the diabetes-induced impaired vasodilation in the current study. The gene discussed is DDAH1; the disease is diabetes mellitus.