The experiments on 60 mongrel rats with hepatic failure due to small intestinal fistulas of high and medium location were carried out for the examination of amino acid spectrum in the animal plasma. 16 free amino acids were studied by ion-exchange chromatography. It has been established that hepatic failure due to small intestinal fistulas is characterized by the reduction of the total amino acid content by 20-30%. These changes were brought about mainly by the reduction of glucoblastic and essential amino acids. A dramatic (400%) increase in His and a slight (20%) increase in Asp were noted in high fistulas. The changes were caused by profound losses through fistulas which markedly activated gluconeogenesis and led to full exhaustion of amino acid reserves. It was concluded that the question of diagnostic amino acid value should be considered taking into account the amount of losses and the activity of gluconeogenesis in the pathogenesis of hepatic failure.