The Omniflow Vascular Prosthesis (OVP) is a truly integrated bio-synthetic composite of polyester mesh and ovine connective tissue components. In animal and human studies, the prosthesis has demonstrated long-term patency rates comparable and often better than alternate surgical replacements, with minimal aneurysmal or thrombotic problems. Immunohistological and TEM analysis of explants of OVP I provide good evidence for the excellent in vivo performance and are reviewed below. In addition, new data from explants of the OVP II, a later version of the Omniflow, are also described. These explant analyses have been enhanced by use of a library of highly specific monoclonal antibodies which can discriminate between collagens from different species.