Serum amino acid concentration measurements in infants with low birth weight fed on human milk or on two humanized formulas and in infants on total parenteral nutrition showed that taurine was significantly decreased in the three groups on artificial diet. Infants weighing more than 2,000 g on total parenteral nutrition perfused with a solution containing no taurine and little cystine showed a low taurine concentration despite a significant increase of cystine. These results favor the hypothesis of Sturman et al., that the human infant cannot synthetize in adequate amount of taurine from cystine and methionine precursors and may be dependent on its diets as a taurine source.