Renal secretion of organic anions plays a critical role in clearing the body of endogenous and exogenous compounds. The organic anion transporters 1 (Oat1), 3 (Oat3) and 5 (Oat5) are mainly located in the kidneys. The modifications in the renal expression of Oat1, Oat3 and Oat5 in renal diseases (chronic and acute renal failure) and in other diseases such as arterial calcinosis and extrahepatic cholestasis have been studied in our laboratory. We have demonstrated the important role of Oat1 expression in the renal elimination of p-aminohippurate (PAH), independently of renal Oat3 expression. In this connection, we have reported that a decrease of Oat1 abundance in basolateral membranes is associated with a diminished PAH renal elimination in experimental models of acute renal failure (ischemia/reperfusion, ureteral obstruction and mercury nephrotoxicity) and in chronic renal failure. Meanwhile, Oat3 abundance in renal basolateral membranes decreased, not changed or increased in these pathologies. On the contrary, Oat1 expression was increased in kidneys from rats with extra-renal pathologies and was associated with an increased in organic anions renal excretion. Our group has been pioneering in the urine detection of Oat5. Oat5 abundance was increased in urine from rats with an early stage of ischemic acute renal failure suggesting that this protein might be a potential early non-invasive marker of this pathology. Actually we are evaluating the urinary excretion of Oat5 in the presence of other diseases in order to determine its possible role as an early biomarker of renal tubular damage.