Background: We hypothesised, that perioperative use of N(2)-l-alanyl-l-glutamine confers cardioprotection and improves insulin resistance in diabetic patients with coronary artery disease operated under cardiopulmonary bypass. Methods: This double-blind, placebo-controlled, randomised study included 64 patients with diabetes mellitus type 2 who were scheduled for on-pump coronary artery bypass graft surgery. The protocol group (32 patients) and the control group (32 patients) glutamine (0.4g/kg/day of 20% solution of N(2)-l-alanyl-l-glutamine (" Dipeptiven^®" Fresenius Kabi, Germany)) and placebo (0.9% NaCl), respectively. Perioperative concentration of troponin I in plasma was considered as the primary end-point. Whereas the secondary end-points were insulin resistance, insulin sensitivity, β-cell function, blood glucose, plasma triglycerides and free fatty acids concentrations. Insulin resistance, insulin sensitivity and β-cell function were measured using HOMA equation. Thermodilution method was used to measure haemodynamics in all the patients. Results: No differences have been found in perioperative dynamics of troponin I, insulin resistance, insulin sensitivity, β-cell function, blood glucose, plasma triglycerides free fatty acids concentrations and haemodynamics. Conclusion: Our results have failed to confirm the cardioprotective properties and modulatory effect on perioperative insulin resistance that are thought to be attributable to parenteral glutamine administration in dose 0.4. g/kg/day among cardiac patients with DM operated on under CPB.