Blood transfusions given to potential renal transplant recipients are beneficial to subsequent graft survival. This study has shown an association graft survival. This study has shown an association between the inhibitory activity of patients' plasma on their own non-specific lymphocyte responses to antigen and the administration of blood transfusions. Most of the inhibitory activity was related to alpha-2 macroglobulin. Alpha-2 macroglobulin was able to prolong the survival of rat cardiac allografts. Immunoregulatory activity related to the alpha globulins of plasma has been described in a wide variety of conditions (i.e. cancer, pregnancy, diabetes) and this study has shown similar activity following blood transfusions.