The effects of L-arginine (L-Arg), the physiological NO precureor and NO synthetase inhibitor NG-nitro-L-arginine (L-NNA) on endogenous endothelin (ET) secretion and renal function were observed in a model of glycerol-induced acute renal failure (ARF) in rat. It was found that endogenous ET secretion was significantly increased, while serum NO was markedly decreased in ARF rats. The administration of L-NNA to the ARF rats induced significant increases in plasma ET and positive immunoreactive particles of ET in renal tubular epithelial cells(EP cells), and the impairment of renal function was exaggerated. L-Arg might effectively decrease the level of plasma ET and the positive immunoreactive particles of ET in renal tubular EP cells, suggesting the improvement of the renal function. It is suggested that the ability of NO in improving renal function may relatedto the inhibition of endogenous ET secretion in glycerol-induced ARF rats.