A controlled clinical trial was made of the anti-ammoniaemic properties of gamma-ethylester glutamic acid, arginine and placebo in a series of 45 patients with hepatic insufficiency characterized by hyperammonemia (excluding cases of pre-coma and coma) randomly assigned to three groups for treatment with: gamma-ethylester of glutamic acid (25 g), l-arginine (25 g) and physiological solution in identical 500 ml bottles. Various parameters were controlled. The results obtained were assessed with different statistical techniques, depending on the parameter concerned and the aims of the trial. Blood ammoniaemia was significantly decreased by both-ethylester of glutamic acid and arginine though the former was more effective quantitatively and in terms of time. SGOT and BSF values also followed the same pattern.