Ten very low birth weight (VLBW) infants (birth weight: 994 +/- 66 g, gestational age: 27 +/- 0.5 wk) requiring total parenteral nutrition (TPN) were studied in order to evaluate their metabolic response to the amino acid solution Travasol 10% blend C. These patients received the solution at a constant rate, providing 2.61 +/- 0.02 g/kg/day of amino acids and 76 +/- 1 kcal/kg/day. Plasma amino acids analysis was performed after 4.6 +/- 0.3 day of infusion and compared to values reported previously with Travasol blend B. The new solution (blend C) showed a significantly lower (p less than 0.001) glycinemia (485 +/- 24 vs 993 +/- 69 mumol/liter), methioninemia (39 +/- 2 vs 114 +/- 12 mumol/liter) and phenylalaninemia (67 +/- 3 vs 92 +/- 5 mumol/liter) related to the lower intake of these amino acids. Despite the provision of 47.5 mmol/liter of serine with blend C no changes in plasma level (182 +/- 15 vs 196 +/- 41 mumol/liter) were noted. The increased molar arginine/glycine ratio (blend C: 0.48 vs blend B 0.22) could have contributed to keep ammoniemia within normal levels (55.1 +/- 4.2 mumol/liter). Wide variations in insulin response (9.9 to 26.4 microU/ml) allowed for a correlation between its plasma concentration and those of sensitive amino acids, underlining its role in protein metabolism. Despite the immaturity of the study population no short-term metabolic imbalance has been encountered with the Travasol blend C solution.