This work results from some research carried out by the authors during the last few years in nutrition field. The data collected allowed to compare protein and lipid composition of infant formulas with human milk and to evaluate the influence of such feedings on plasma aminoacid levels and erythrocyte fatty acids. In spite of different infant formula compositions with respect to human milk, our nutritional studies did not demonstrate physiological differences between breast and bottle-fed infants if formulas provide with an adequate intake of protein and linoleic acid.