Objective: Free radical production is increased by the administration of total parenteral nutrition (TPN) and may be linked to its adverse effects. Some of the complications of TPN can be ameliorated by partial enteral feeding. In the present study, we investigated plasma nitrate/nitrite (NO2/NO3) levels in newborns under parenteral and enteral plus parenteral nutrition (PN). Study Design: Six categories of patients were studied: (1) 10 term infants receiving enteral feeding, (2) 10 term infants receiving PN plus enteral feeding, (3) 10 term infants receiving TPN, (4) 10 preterm infants receiving enteral feeding, (5) 10 preterm infants receiving PN plus enteral feeding, and (6) 10 preterm infants receiving TPN. Plasma nitrate/nitrite levels were measured in all infants initially and in infants receiving TPN and PN plus enteral feeding on the 1st and 5th days, 3 h after the lipid infusion. Results: There was a statistically significant difference in the weighs of infants between the term and preterm groups. There was no difference in NO2/NO3 levels between the term and preterm groups. When the groups of term (groups 1, 2, 3) and preterm (groups 4, 5, 6) infants were compared separately within the groups, no statistically significant difference was found in any parameters. We also made comparison among the six groups' gestational ages, and we found a difference between all term groups and all preterm groups except between groups 1 and 2; groups 1 and 3; groups 2 and 3; groups 4 and 5, and groups 5 and 6 (p < 0.05). Furthermore, the baseline, 1st and 5th days NO2/NO3 levels were compared in the term and preterm groups receiving PN. Plasma NO2/NO3 levels before TPN were significantly lower in the term infants receiving parenteral fluids compared with NO2/NO3 levels of 1st day of TPN (p < 0.05). In preterm infants receiving TPN the NO2/NO3 levels before TPN were significantly lower than the levels on the 5th day of PN (p < 0.05). There was no significant difference among other NO2/NO3 levels of the patients at baseline, 1st and 5th days in the term and preterm groups. Partial enteral feeding did not change the levels of NO2/NO3 in term and preterm infants on PN. Conclusion: This study shows that TPN has some impact on nitric oxide (NO) production in newborn and partial enteral nutrition does not reduce this effect. However, since the numbers are very small these findings need to be verified by larger groups of patients. Copyright (c) 2007 S. Karger AG, Basel.