Acute renal failure still remains an important and challenging problem in the ICU. Hemodialysis is not always feasible because of hemodynamic instability in critically ill patients. In this circumstances continuous arteriovenous hemofiltration (CAVH) can be an efficient alternative as this method has less detrimental hemodynamic effects. Moreover, within certain limitations, CAVH proves to be an effective "artificial kidney" (control of body fluid, electrolyte and acid-base homeostasis and uremia) and this without serious side-effects. Special emphasis is made on the problem of anticoagulation, which can cause life-threatening complications in posttraumatic and surgical patients. A protamine infusion on the venous line can diminish these complications.