The development of computerized machines with a simple user-friendly interface to perform continuous venovenous hemodiafiltration (CVVHDF) has resulted in a break-through of CVVHDF in the treatment of acute renal failure (ARF) in Danish intensive care units. During CVVHDF the blood is submitted to a combination of dialysis and ultrafiltration. In contrast to intermittent haemodialysis (HD), CVVHDF can be used in critically ill patients with unstable circulation. Biocompatible membranes are used. During treatment with CVVHDF, cytokines are removed from the blood partly by ultrafiltration, partly by adsorption to the filter. The clinical importance of this is not yet known. Patients with ARF treated with CVVHDF seem to be more likely to show renal recovery than those treated with HD. There are few prospective investigations of the effect of CVVHDF on mortality, but all comparisons of CVVHDF with HD indicate a trend in favor of CVVHDF.