The authors present values of plasma amino acid concentrations assessed on an automatic analyzer in a group of 12 mature neonates whose early and late post-partum adaptation and subsequent psychosomatic development followed-up to the age of 18 months was normal. The amino acids were assessed at the time of delivery, during the maximal weight loss of the infant after the third day and the last estimation was made before discharge from the maternity hospital when the body weight curves of all infants had a rising trend. None of the infants had neonatal jaundice and all were discharged fully breastfed.