Acute kidney injury is an important complication in hospitalized patients often diagnosed late and associated with high mortality and morbidity. Although biomarkers for nephrotoxicity are available, they often lack sensitivity and specificity for detecting tubular injury. Netrin-1 is a laminin like molecule highly expressed in many organs including kidney. To determine the value of netrin-1 as a biomarker of renal injury, we analyzed its urinary excretion following ischemia reperfusion, cisplatin, folic acid and endotoxin induced renal injury in mice. Urinary netrin-1 levels increased markedly within 3 hours of ischemia reperfusion (40±14 fold, p0.01 vs. baseline), reached a peak level at 6 hours and decreased thereafter, returning to near baseline by 72 hours. Serum creatinine significantly increased only after 24 hours of reperfusion. Similarly, in cisplatin, folic acid and lipopolysaccharide treated mice, urine netrin-1 excretion increased as early as 1 hour and reached a peak level at 6 hours after injection. However, serum creatinine was raised significantly after 6, 24 and 72 hours after folic acid, lipopolysaccharide and cisplatin administration respectively. NGAL excretion in folic acid and lipopolysaccharide treated mice urine samples could only be detected by 24 hours after drug administration. Furthermore, urinary netrin-1 excretion increased dramatically in 13 acute renal failure patients whereas none was detected in 6 healthy volunteer urine samples. Immunohistochemical localization showed that netrin-1 is highly expressed in tubular epithelial cells in transplanted human kidney. We conclude that urinary netrin-1 is a promising early biomarker of renal injury.