Neonatal respiratory distress syndrome (RDS) is characterized by an immature surfactant phospholipid pattern. We aimed to study the evolution of surfactant phospholipids over a 6-day period, before and after surfactant replacement therapy with Curosurf, and to investigate possible interactions with exogenous phospholipids administered during total parenteral nutrition (TPN). Seventeen premature infants with RDS were randomly assigned to receive TPN with lipids or without (glucose group). Both groups showed a similar evolution of the surfactant phospholipids. At day 6, the surfactant composition had changed towards a mature human surfactant pattern except for phosphatidylglycerol which remained low (1%), compensated for by a high phosphatidylinositol and phosphatidylserine proportion (13.3%), Phospholipid subcomponents in plasma remained unchanged in both groups. Plasma total cholesterol (151 +/- 18 vs. 113 +/- 6 mg/dl, p less than 0.05) and cholesteryl esters (172 +/- 20 vs. 113 +/- 9 mg/dl, p less than 0.01) were higher in the glucose than in the lipid group. Total calorie intake was significantly higher in the lipid group (85 +/- 4 vs. 64 +/- 6 kcal/kg.day, p less than 0.01).