Ischaemia-reperfusion (IR) injury makes a major contribution to graft damage during kidney transplantation and increases the risks of primary non-function, delayed graft function and rejection. Oxidative damage to mitochondria is a key early event in IR injury. The aim of this project was to examine the safety and efficacy of the mitochondria-targeted antioxidant MitoQ in reducing pig and human kidney IR injury using an ex vivo normothermic perfusion (EVNP) system. Over a range of 500 nM to 250 µM using a 150 pig kidneys and 80 declined deceased human kidneys, MitoQ was successfully taken up by pig and human kidneys in a concentration-dependent manner, resulting in stable tissue concentrations over 24 hours of cold storage followed by 6 hours of EVNP. The uptake of MitoQ was increased approximately 2-fold when MitoQ was administered to warm (rather than cold) kidneys and when kidneys were preserved using hypothermic machine perfusion (rather than cold static storage). 50 µM MitoQ, administered to pig kidneys at the end of warm ischaemia, significantly increased renal blood and urine output flow at the end of 6 h EVNP compared to the control group. Creatinine clearance was numerically higher in the 50 µM MitoQ group compared to the control group but the difference did not reach statistical significance. To test the safety and efficacy of MitoQ in human kidney IRI, pairs of declined deceased human kidneys were used, with one kidney in each pair used as control. The total urine output, creatinine clearance and percentage fall of serum creatinine were numerically higher in the 50 µM MitoQ group compared to the control group, although the differences did not reach statistical significance during 3 h of EVNP. There was a significant difference in the renal blood flow between the 50 µM MitoQ group and the control group at the end of the first hour of EVNP. The renal blood flow remained relatively stable during the first hour of EVNP in the 50 µM MitoQ group compared to a significant decrease in renal blood flow in the control group. There was no effect on fractional excretion of sodium or oxidative injury markers (protein carbonyl formation, lipid peroxidation) in pig or human kidneys, which is consistent with previous studies that demonstrated the requirement of >24 hour after reperfusion for manifestation of changes in these parameters. In this thesis, I was able to successfully demonstrate the safety and potential efficacy of MitoQ in ameliorating renal IRI using pig kidneys. While more declined deceased human kidneys need to be analysed to fully explore the potential efficacy of MitoQ in ameliorating renal IRI, this study provides important data that will help inform future studies and ultimately a clinical trial for assessing the efficacy of the mitochondria-targeted antioxidant MitoQ in human kidney transplantation. My findings suggest that MitoQ has the potential to increase the use of marginal kidneys and to improve graft and patient outcomes.