This study was designed to compare growth parameters, biochemical indices of protein metabolism and serum amino acid patterns in newborn infants fed either human milk (n: 22) or formula with protein and amino acid concentrations similar to human milk (n: 19) during the first two months of life. Growth parameters were normal and similar in all infants. Serum levels of transferrin and IgG were not significantly different, whereas prealbumin concentrations were found to be significantly higher in infants fed formula compared to those fed human milk. In the formula group, glutamic acid and cystine levels were significantly lower while phenylalanine and proline were significantly higher compared to the breastfed group. It was observed that feeding a formula with an amino acid pattern similar to that of human milk does not necessarily give rise to identical patterns of amino acids or indices of protein metabolism.