A new amino acid solution (Aminopäd 5% and Aminopäd 10%) was used for intravenous feeding of 240 preterm and term newborn infants in 4 hospitals. Indications, dosages and infusion sites were up to the policies of the 4 hospitals. Plasma amino acid concentrations were measured in 491 samples which were obtained during steady 24 h infusions of the daily doses. Results were analyzed in four subgroups formed according to the postmenstrual ages of the patients at the time of blood withdrawal and showed good agreement with the reference values. Acute cholestasis was observed in 22 infants which could be explained by bacterial infection alone in 18 patients.