OBJETIVE: Considering that in malnourished patients supplemented with L-glutamine the negativity of the nitrogen balance tends to decrease, the present study aimed to determine whether malnourished Wistar rats supplemented with L-glutamine would show lower urinary nitrogen excretion, a greater deposition of nitrogen content in different tissues, and/or an alteration in the plasma amino acid levels. METHODS: The rats were divided into groups: 1) protein-energy malnutrition, 2) protein malnutrition and 3) normally nourished group. The urinary and tissue nitrogen contents were determined by the Kjeldahl method and plasma amino acids by liquid chromatography. RESULTS: Weight, urinary and tissue nitrogen accumulation were significantly reduced in the group with protein-energy malnutrition, but did not improve with L-glutamine supplementation supplied for a short time. The plasma amino acid concentrations showed no special pattern with L-glutamine supplementation. CONCLUSION: It was concluded that it was not possible to detect any positive effect of L-glutamine supplementation on the tissue and urinary nitrogen metabolism in malnourished rats.