The protein fractions of lumbar cerebrospinal fluid (CSF) were studied in 40 normal newborns 2 days-old. The results were compared to those found in normal adult peoples. It was shown that the relative concentrations of albumin, alpha-1 globulin, and gamma globulin are more conspicuous in the newborn than in the adult. The protein pattern in the normal newborn is similar to the transudative pattern described in the adult life in several pathologic conditions. The findings were related to the blood — CSF barrier conditions in the newborn. The incomplete functional maturity of blood — CSF barrier at this time of the life was considered to be the main factor responsible by the CSF protein pattern which was found.