AIM: To evaluate whether the effect of Gln dipeptideenriched total parenteral nutrition (TPN) on postoperative cytokine alteration depended on the disease severity of surgical patients.METHODS: Forty-eight patients with major abdominal surgery were allocated to two groups to receive isonitrogenous (0.228 g nitrogen/kg per d) and isocaloric(30 kcal/kg per d) TPN for 6 d. Control group (Conv)using conventional TPN solution received 1.5 g amino adds/kg per day, whereas the test group received 0.972 g amino acids/kg per day and 0.417 g L-alanyl-L-glutamine(Ala-Gln)/kg per day. Blood samples were collected on d 1 and d 6 postoperatively for plasma interleukin (IL)-2,IL-6, IL-8, and interferon (IFN)-γ analysis.RESULTS: Plasma IL-2 and IFN-γ were not detectable.IL-6 concentrations were significantly lower on the 6th postoperative day in the Ala-Gln group than those in the Conv group in patients with APACHE Ⅱ≤6, whereas no difference was noted in patients with APACHE Ⅱ＞6. There was no difference in IL-8 levels between the two groups.No difference in cumulative nitrogen balance was observed on d 2-5 after the operation between the two groups(Ala-Gln -3.2±1.6 g vs Conv -6.5±2.7 g). A significant inverse correlation was noted between plasma IL-6 levels and cumulative nitrogen balance postoperatively in the Ala-Gln group, whereas no such correlation was observed in the Conv group.CONCLUSION: TPN supplemented with Gln dipeptide had no effect on plasma IL-8 levels after surgery. However,Gln supplementation had a beneficial effect on decreasing systemic IL-6 production after surgery in patients with low admission illness severity, and lower plasma IL-6 may improve nitrogen balance in patients with abdominal surgery when Gln was administered.