A major hurdle to adenovirus (Ad)-mediated gene transfer is that the target issue lacks sufficient levels of receptors to mediate vector attachment via its fiber coat protein. Endothelial and smooth muscle cells are primary targets in gene therapy approaches to prevent restenosis following angioplasty or to promote or inhibit angiogenesis. However, Ad poorly binds and transduces these cells because of their low or undetectable levels of functional Ad fiber receptor. The Ad-binding deficiency of these cells was overcome by targeting Ad binding to alpha v integrin receptors that are sufficiently expressed by these cells. In order to target alpha v integrins, a bispecific antibody (bsAb) that comprised a monoclonal Ab to the FLAG peptide epitope, DYKDDDDK, and a monoclonal Ab to alpha v integrins was constructed. In conjunction with the bsAb, a new vector, AdFLAG, which incorporated the FLAG peptide epitope into its penton base protein was constructed. Complexing AdFLAG with the bsAb increased the beta-glucuronidase transduction of human venule endothelial cells and human intestinal smooth muscle cells by seven- to ninefold compared with transduction by AdFLAG alone. The increased transduction efficiency was shown to occur through the specific interaction of the complex with alpha v integrins. These results demonstrate that bsAbs can be successfully used to target Ad to a specific cellular receptor and thereby increase the efficiency of gene transfer.