The blood-brain barrier (BBB) was studied in 76 neonates of different gestation age in health and disease by means of detecting specific alpha-1-globulin in blood serum with the aid of ELISA. It has been established that by week 28 of the intrauterine development the process of the structural and functional establishment of the BBB had been over as evidenced by the lack of specific alpha-1-globulin in umbilical blood of the neonates of the given gestation age. Severe chronic intrauterine hypoxia combined with acute hypoxia resulted in brain damage and BBB opening for antigen penetration in the direction brain-blood. The measurement of the concentration of alpha-1-globulin in the course of observing the neonates made it possible to predict the degree of the CNS damage.