We have developed simultaneous plasmacollection and exchange using membrane plasma separators, as a useful therapy for hepatic failure. By this method, the loss of effectiveness of fresh plasm is very small and larger amount of plasma can be obtained from the donor very safely. In the experiments here, we evaluated the effect of this therapy, using D-galactosamine induced hepatic failure beagle dogs as a model of acute hepatic failure. The effect was indicated by the remarkable decline of those increasing factors such as transaminases, and by the recovery to some extent, of coagulation factors.