We studied the ability of adenoviral vectors to achieve gene transfer into injured arteries. A recombinant adenoviral vector expressing a nuclear-targeted β-galactosidase gene was constructed and infused into balloon-injured rat carotid arteries. Three days after gene transfer, recombinant gene expression was assessed quantitatively by (1) measuring β-galactosidase antigen and activity in tissue extracts and (2) histochemical staining and counting of cells expressing β-galactosidase. Exposure of injured carotid arteries to increasing concentrations of the vector (108 to 1010 plaque-forming units per milliliter) resulted in a dose-responsive increase in β-galactosidase expression, with peak expression of approximately 43 mU or 25 ng β-galactosidase per vessel. Microscopic examination of histochemically stained arteries demonstrated gene transfer limited to the vascular media; transduced cells were identified immunohis-tochemically as smooth muscle cells. Counting of both histochemically stained and total nuclei in the media revealed that approximately 30% of the cells in the media of the injured vessels were transduced. Calculations based on both counting cells and on the level of β-galactosidase expression in tissue extracts suggested the presence of 5000 to 10 000 transduced cells per 10 mm of vessel. Arteries infused with either vehicle only, a control adenoviral vector, or liposomes combined with the vector plasmid contained little or no evidence of β-galactosidase expression. High levels of in vivo β-galactosidase expression persisted for at least 7 days after gene transfer but declined significantly by day 14. We conclude that adenoviral vector-mediated gene transfer into the injured rat carotid artery results in efficient gene transfer into the vascular media, with levels of recombinant protein production significantly higher than any previously reported in arterial gene transfer studies. Adenoviral vectors appear to be particularly useful agents for in vivo arterial gene transfer.