The potential of gene therapy to deliver therapeutic protein agents, such as cytokines, antibodies and recombinant ligands, in vivo has stimulated interest in many biological fields, including transplantation. Regarding the latter, gene transfer strategies could be used to deliver molecules with immunomodulating activity to the graft itself or to defined sites in the recipient to prevent graft rejection or ischaemic injury or to induce tolerance to donor alloantigens. Any of these options offers many advantages over the systemic delivery of immunosuppressive agents currently employed in transplantation.