WITH THE continuing development of newer and more sophisticated scientific techniques for evaluating the functions of the vital organs, it was inevitable that organ substitution techniques would also be developed, and that replacement of defective organs by functioning mechanical and human organs would become a procedure to save and prolong life. It is this prolongation of life to which this presentation is directed, focusing specifically on patients with chronic renal failure whose lives are prolonged by chronic hemodialysis and kidney transplantation. It is essential to keep in mind that prolongation of life involves not only adding time to the length of life, but it also involves the matter of the quality and worthwhileness of the life that is thus prolonged. Patients with renal failure fear that their lives will be cut short by an untimely death, and as we listen closely we also