There are a great deal of data concerning the role of testosterone in the formation of the sex of the fetus. The synthesis of the testosterone is influenced by the hypophysis and the fetoplacental unit. In this study the authors conferred the progesterone, DHAS, cortisol, oestradiol, oestriol, prolactin and HPL levels of male and female newborns in the maternal vein and in the umbilical vein and artery in the 28th-32th weeks (31 parturients, 15 male and 16 female fetuses), in the 33rd-36th weeks (43 parturients, 20 male and 23 female fetuses) and in the 40th week (34 parturients, 11 male and 23 female fetuses) of pregnancy. The determination of serum hormone concentration was carried out with the RIA method in 2084 samples. There was no significant difference between the serum hormone concentrations of the male and female sex in the 28th-40th weeks of pregnancy. They assume that in the 28th-40th weeks there is no difference in the activity of steroid and peptide hormone secretion caused by the sex of the fetus.