The identification of immunomodulatory approaches that allow the induction of antigen-specific unresponsiveness is required for long-term graft survival without the complications of chronic immunosuppression. Recent novel strategies based upon treatment with synthetic peptides corresponding to linear sequences of MHC class I and II molecules reproducibly induce tolerance to alloantigens. Although the mechanisms involved are still not completely understood, the phenomenology reported makes these approaches promising for evaluation in clinical trials.