“…Thus, the patient whose course is shown in Figure 1 required relatively massive doses of prednisone early in his convalescence, but steroid treatment was subsequently stopped without deterioration of homograft function. In animal laboratories, it has been shown (21, 25,27,[30][31][32]35) that all treatment may be discontinued in some recipients of whole-organ homografts with survival for many years. We have observed examples of this kind of "graft acceptance" after initial immunosuppressive treatment with 6-mercaptopurine, azathioprine, and heterologous antilymphocyte serum.…”