Erectile dysfunction (ED) is a cause of decreased quality of life in more than 70% of diabetic men. Vascular endothelial growth factor (VEGF) has shown to improve overall endothelial and smooth muscle cell dysfunction in models of ED. We describe a novel technique for nonviral, in vivo gene transfection of VEGF in the rat corpus cavernosum. Diabetic rats were transfected with DNA encoding a fusion VEGF/green fluorescent protein (GFP) complex and fluorescence microscopy was used to monitor the expression of VEGF-GFP fusion protein. Western blot and PCR analyses confirmed the expression of the GFP-VEGF fusion protein and mRNA. Functional studies using cavernous nerve stimulation revealed maximal intracavernous pressures (ICPs) of 63.1 mm Hg, and 30.7 mm Hg in the normal and diabetic control groups, respectively, and 47.4 mm Hg in VEGF-GFP-transfected diabetic group. Immunohistochemical analysis of the cavernosal tissue from transfected rats showed increased smooth muscle content compared with the diabetic control group. We show for the first time in our animal model that expression of the transfected VEGF in cavernosal tissue leads to an overall improvement of maximal ICP and smooth muscle content. On the basis of these results, it is tempting to speculate that our nonviral vector system offers an excellent system for gene delivery into cavernosal tissue, and that VEGF gene therapy using this system could be useful in improving erectile function in diabetic men.