27 patients admitted for elective abdominal surgery were allocated to receive postoperative total parenteral nutrition supplemented with glutamine (glycyl-glutamine) and tyrosine (glycyl-tyrosine) containing dipeptides (DP-Gln 20; 0.16 g glutamine/kg BW/24 h) or isonitrogenous Vamin 18 for 5 days. The aim was to evaluate safety and effects on short-life plasma proteins, nitrogen balance, 3-methylhistidine excretion and alimentary growth factors in plasma. No differences in transthyretin or retinol binding protein levels, nitrogen balance or 3-methylhistidine excretion were found in patients receiving DP-Gln 20 compared to Vamin 18. There were higher plasma levels of peptide YY in the dipeptide group 5 days after surgery (p < 0.05). A correlation between insulin levels and nitrogen balance was found only in DP-Gln 20 treated patients day 6 (r = 0.91, p < 0.01). DP-Gln 20 is a glutamine dipeptide (Gly-Gln) containing amino acid solution which is considered safe in the postoperative state in man. No beneficial effects on whole body protein metabolism were found by adding DP-Gln 20 to total parenteral nutrition.