The relative importance of the various retained metabolites in the production of the uremic syndrome has yet to be elucidated (1). Although in most instances uremia is the terminal evidence of irremedial kidney damage, the existence of a group of conditions leading to acute, reversiblerenal in-sufficiency necessitates a mechanism for maintain-ing life during the period of repair. This temporary compensation for renal failure has been attempted in several ways, the most important of which are:(a) peritoneal lavage (2-4)(b) intestinal lavage (5, 6)(c) various types of" artificial kidneys." Abel, Rowntree, and Turner in 1914 introduced the first" artificial kidney," dialyzing the blood of experimental animals through celloidin tubes, using hirudin as an anticoagulant (7). They realized the potentialities of this basic idea, but it has been only recently with the development of (a) effective anticoagulation with heparin, and (b) improved dialyzing membranes, that this same fundamental method has been of practical impor-tance. It remained for Kolffto pioneer in the construction ofa dialyzing apparatus proving to be successful in the therapy of uremia in man (8). This apparatus consisted of a long cellophane tube wound spirally about a large drum, which revolved horizontally in a bath of the dialysate. Blood was introduced into the tube from the radial artery and returned by a pump to an antecubital vein. Simultaneously with this important development in Holland, work was being carried out independently in Sweden by Alwall (9) and in Canada by