Abstract. Objective: To analyze amino acid profiles and serial blood urea nitrogen values (BUN) in infants <1250 g receiving early amino acid infusion within hours of birth and compare them to previously published values. Design/methods: A retrospective study was conducted on infants <1250 g admitted to the NICU between July 2009 to July 2010. Plasma amino acid (AA) profiles were analyzed by high-performance liquid chromatography and values were compared to previously established reference values. Demographic data, treatment with indomethacin or neoprofen and laboratory results were also collected. Results: A total of 40 neonates were studied. Thirty infants had a single plasma sample and 10 infants were followed with serial samples. AA profiles were consistent with previously published reference values. Serial samples showed little change over 3 days of infusion. Increased BUN did not correlate with abnormal AA profiles or concentration of AA infused in the infants studied. Conclusions: AA profiles on infants <1250 g on exclusive total parenteral nutrition on DOL1-3 demonstrated no evidence of hyperaminoacidemia with the exception of asparagines, threonine and lysine that were below reference levels. A small subset of infants with elevated BUN, demonstrated similar aminograms to those with lower BUN value even when being treated for a symptomatic PDA. Early TPN appears to be well tolerated by extremely preterm infants.