For both in vitro and in vivo experiments, especially in vascular cells, an efficient and easy method of gene transfer into this tissue would be extremely useful. Previous methods have either yielded low levels of expression or require complicated manipulation of viral vectors. The goal of this study was to develop an easy, efficient method to introduce unmodified plasmid DNA into vascular tissue. In this report it is demonstrated that complexing unmodified plasmid DNA with replication-deficient adenovirus (Ad5 dl312) via cationic lipids enhances gene transfer up to 1000-fold in cultured bovine aortic endothelial cells (BAECs). Further, utilizing a balloon-injured rabbit femoral artery model, intense nuclear staining in both the neointimal smooth muscle cell layer and the adventitia was seen following transfection with a plasmid containing the lacZ gene and the SV40 nuclear localization signal. Control arteries demonstrated no detectable staining. Our studies suggest that complexing plasmid DNA with adenovirus via lipids greatly enhances gene transfer both in vivo and in vitro. This method could have a wide range of applications for experiments in vascular tissue.