SummaryAmino acid metabolism is compared in normal subjects and in uraemia. Principal modifications in plasma concern essential amino acids. Elevation of phénylalanin/ tyrosine ratio is always observed in uraemia. It results from a deficiency in phenylalanine hydroxylase. Tissue distribution of amino acids is also modified. Urinary loss in essential amino acids are not great except when a Fanconi syndrome is present. The greatest loss are due to hemodialysis. Patients suffering from uraemia need more essential amino acids. Supplements are necessary with diets poor in proteins. Some amino acid accumulated in plasma could contribute to the uraemic intoxication but this point is not demonstrated.