There is now unequivocal evidence for the existence of CD4+T cells that can suppress transplant rejection. If the developmental origins and special diagnostic features of such cells could be understood, then it might be possible to selectively harness their properties for therapeutic purposes. Here we review recent information on their properties and speculate that it may soon be possible to selectively manipulate the immune system so as to empower such T cells so that they might dominate those that would otherwise reject the transplant.