The authors report the results of the immunonephelometric determination of 9 proteins in the serum of 74 newborns: CRP, orosomucoid, haptoglobin, alpha-1-antitrypsin, C3, C4, transferrin, prealbumin and apo B have been studied. The influence of gestational and postnatal ages are shown. Results are compared with those of the literature. The respective role of the transfer of plasma proteins from mother to foetus and of foetal synthesis in the concentration of a protein in the serum of a neonate is discussed.