Although glycine prevents renal tubular cell injury in vitro, its effect in vivo is not clear. The purpose of this study was to investigate whether a bolus injection of glycine given before reperfusion plus continuous dietary supplementation afterward would reduce renal injury caused by ischemia-reperfusion. Female Sprague-Dawley rats received a semisynthetic powdered diet containing 5% glycine and 15% casein (glycine group) or 20% casein (control group). Two days later, renal ischemia was produced by cross-clamping the left renal vessels for 15 min, followed by reperfusion. The right kidney was removed before reperfusion. The postischemic glomerular filtration rate (GFR) showed that renal function was less impaired and recovered more quickly in rats receiving glycine. For example, at day 7, GFR in controls (0.31 ± 0.03 ml · min¹ · 100 g¹) was about one-half that of glycine-treated rats (0.61 ± 0.06 ml · min¹ · 100 g¹, P < 0.05). Furthermore, tubular injury and cast formation observed in controls was minimized by glycine (pathology score, 3.2 ± 0.4 vs. 1.0 ± 0.4, P < 0.05). Urinary lactate dehydrogenase (LDH) concentration was elevated by ischemia-reperfusion in the control group (260 ± 22 U/l), but values were significantly lower by about fourfold (60 ± 30 U/l) in glycine-fed rats. Similarly, free radical production in urine was significantly lower in glycine-treated animals. Importantly, on postischemic day 1, binding of pimonidazole, an in vivo hypoxia marker, was increased in the outer medulla in controls; however, this phenomenon was prevented by glycine. Two weeks later, mild leukocyte infiltration and interstitial fibrosis were still observed in controls, but not in kidneys from glycine-treated rats. In conclusion, these results indicate that administration of glycine indeed reduces mild ischemia-reperfusion injury in the kidney in vivo, in part by decreasing initial damage and preventing chronic hypoxia.