Beneficial effects of glutamine on wound healing are well known. Parenchymal injuries in the lung cause air leakage that resolves with wound healing. We aimed to determine the effect of glutamine on the healing of lung injuries. Wistar albino female rats were randomized in three groups. One group (control, n = 7) received intraperitoneal injection of 0.9% sodium chloride (1.5 ml /day), while other group (GLN, n = 7) received glutamine (1.5 g/kg/day), beginning two days prior to the operation for total four days. After thoracotomy, a lung parenchymal lesion was made with a scalpel in the right upper lobe. Only thoracotomy was performed to sham group (n = 4). Air leakage was observed in the isolated lungs of control group, but not GLN and sham groups, at 5 cm H(2)O of positive airway pressure (p < 0.001). The threshold of positive airway pressure for air leakage was 4.85 +/- 0.37 and 19.42 +/- 4.54 cm H(2)O for control and GLN groups, respectively (p < 0.001). For measurement of collagen content in the healing parenchyma, digital images were processed to calculate the stained area percentage (SAP). SAP for immature collagen, a marker for wound healing, was 0.36 +/- 0.18% and 1.48 +/- 0.83% (p = 0.02) in control and GLN groups, respectively, but no significant difference was noted in SAP for mature collagen. The grade of inflammation was not significantly different between control and GLN groups. We conclude that glutamine enhances lung parenchymal healing by increasing immature collagen secretion.