The AA. describe a method of gradual occlusion of the portal vein in the rat to induce a hepatic encephalopaty. This method allows to realise a condition of hepatic ischemia and a portal hypertensive state accompanied by spontaneous portal-systemic shunts. These two factors produce a hepatic encephalopaty like in cirrhotic state or in patients after portal systemic anastomosis. A part from similar behavior at the beginning of the encephalopaty it is possible to define two classes of animals: one showing a slow recovery and one showing a transient and slight improvement followed at the end by the death of the animal. The AA. found a definite correlation amoung the clinica, EEG's, serum aminoacids and biochemical data. Probably the different anatomical and phisiological aspects of the induced portal systemic shunts and the different ways of hepatic rivascularization may determine the two different evolutions of the animals.