We have achieved smooth homeostasis in patients with acute renal and respiratory failure by means of machine-controlled, continuous ultrafiltration and simultaneous bicarbonate hemodialysis with a polysulfone, biocompatible membrane (CUPID). No adverse effects were seen, even after 22 days of continued treatment. Mortality was reduced (7/14) when compared to that of a similar group given short conventional daily acetate hemodialysis and ultrafiltration with a cuprophane membrane (12/18).