Abstract: Antibodies directed against idiotypes on naturally occurring human anti-animal antibodies are disclosed for use in inhibiting xenograft rejection in human patients. An effective quantity of these anti-idiotypic antibodies is injected into the actual or potential xenograft recipient in order to bind to the idiotypes expressed on anti-animal antibodies as well as subpopulations of B lymphocytes, to inhibit hyperacute rejection of transplanted animal tissues or organs by the human patient. Alternatively, anti-idiotypic antibodies are used in the form of immunoaffinity columns to deplete anti-animal antibodies from the recipient's serum. Methods of making mouse monoclonal, mouse recombinant, and human recombinant anti-idiotypic antibodies are described, as well as immunoaffinity columns containing immobilized anti-idiotypic antibodies.