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 h of ischemia-reperfusion (40 +/- 14-fold, P < 0.01 vs. baseline), reached a peak level at 6 h, and decreased thereafter, returning to near baseline by 72 h. Serum creatinine significantly increased only after 24 h of reperfusion. Similarly, in cisplatin-, folic acid-, and lipopolysaccharide-treated mice, urine netrin-1 excretion increased as early as 1 h and reached a peak level at 6 h after injection. However, serum creatinine was raised significantly after 6, 24, and 72 h 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 h 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.