Although there have been dramatic advances in clinical organ transplantation over the past 20 years, rejection, both acute and chronic, and the complications of immunosuppression remain major problems. Nevertheless as our understanding of the immune response to a vascularized organ allograft develops, so too will our ability to develop more specific immunosuppression. In any strategy for more specific immunosuppression compatibility for the major histocompatibility complex of antigens (HLA in man) is likely to be important. Monoclonal antibodies to T cell subpopulations, or even to T cells specifically activated by the graft, provide methods of suppressing the immune response at a more specific level. The recognition that stable grafts are maintained, at least in experimental rodent models, by T suppressor cells may allow development of precise methods of inducing the generation of such cells in clinical practice. The induction of tolerance in the adult animal can be achieved in a number of ways, the most promising of which for clinical application, is antigen pretreatment. If tolerance could be achieved in clinical practice within the not too distant future, then this would represent the attainment of the ultimate goal of transplantation.