Abstract. The effect of acute pretreatment with a single dose of simvastatin (1 mg / kg, i.v.; 30 min before ischemia) on renal dysfunction caused by ischemia-reperfusion (I / R) injury in the rat was investigated. I / R injury was induced by clamping both renal vascular pedicles for 45 min, followed by 4 h of reperfusion with saline (2 ml / kg per hour). Simvastatin significantly improved both parameters of glomerular and tubular dysfunction (e.g., creatinine levels and fractional excretion of Na + , respectively) and especially improved the histological score, compared to control I / R-injured rats treated with saline or 10% DMSO only.Keywords: simvastatin, ischemia-reperfusion renal injury, acute renal failure Statins (3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors) were convincingly shown to produce both lipid-lowering-dependent and -independent effects (1, 2). The later effects still remain to be clarified, being attributed to their antiinflammatory, antioxidant, and/ or vascular actions. In several studies, the effects of statins in ischemia-reperfusion (I / R) models of renal protection have been related to upregulation of endothelial nitric oxide synthase (eNOS) and increased production / release of NO. Statins were shown to reduce monocyte and macrophage-related expression of soluble intercellular adhesion molecule-1; lipopolysaccharideinduced secretion of tumor necrosis factor-α, interleukin-6, and inducible NOS (iNOS); and inhibition of NADPH oxidase-dependent superoxide anion production. Also, statins reduced sepsis-related vascular permeability in mice probably via increasing the activity of vascular eNOS (3 -6).