The results of clotting tests during plasmapheresis in 3 cases of acute viral liver necrosis are reported. Elevated F VIII levels were found in all cases before the start of plasmapheresis. During plasmapheresis, a decrease of F VIII activity was found in 2 cases. In the third patient with persistently high F VIII levels during several days of plasmapheresis, disseminated intravascular coagulation may have been present. The mechanisms of the elevation of F VIII in acute viral liver necrosis and the influence of plasmapheresis on F VIII levels are discussed.