Because restenosis represents a crucial clinical application for which endovascular access is available, we evaluated impact of US-mediated enhancement of gene delivery in a rabbit model of arterial mechanical overdilation injury. Because toxicity of gene delivery increases with dose for either plasmid or adenovirus, we selected safer doses that would be subtherapeutic without US enhancement. Blue fluorescent protein expression was used to monitor gene delivery efficiency after femoral angioplasty, and plasmid- or adenoviral-mediated gene delivery with or without endovascular US and was compared to control (saline) treatment. As expected, no statistically significant differences in BFP expression occurred among plasmid, adenoviral and PBS groups at these doses without US (p > 0.05). Prior work has shown that 0.1 μM BFP molecules, approximately 105 copies per cell of 1 to 2 pl volume (15), are needed to surpass detectable endogenous autofluorescence of a mammalian cell. The delivery efficiencies of plasmid and low-dose adenovirus, while not strictly zero, do not yield statistically significant increases in signal intensity relative to these sensitivity thresholds. The impact of US on these efficiencies was tremendous. After US exposure, plasmid-mediated BFP expression increased 12-fold over plasmid control (p < 0.05), and adenoviral-mediated BFP expression increased 19-fold over adenoviral control (p < 0.05). Given low baseline plasmid and adenoviral-mediated gene delivery efficiencies at the doses employed here, it is promising that high copy numbers per cell (at least 105) can be achieved with in vivo US exposure. But the most interesting result is that US increased BFP expression for plasmid relative to adenoviral treatment alone (p < 0.025). Given the cost, handling and safety advantages of plasmid-mediated gene delivery, these results are particularly exciting. Although the present study selected 16 min incubation total for gene transfer, transducer design alone (i.e., to the length of desired transfection) should allow reduction to a single 4-min increment to achieve the observed results. Dose-response studies may offer still further enhancements with accompanying reductions in transfection time.