Endothelin-1 is now known to synthesized in the kidney and influence the renal function. ET-1 mRNA was detected in glomerulus and inner medullary collecting ducts using RT-PCR technique. ETA receptor mRNA was detected only in glomerulus, vasa recta bundle, and arcuate artery. ETB receptor mRNA distributed mainly in glomerulus and collecting ducts. Endothelium derived relaxing factor (EDRF) was believed to be nitric oxide, was synthesized by nitric oxide (NO) synthase from L-arginine. NO stimulates soluble guanylate cyclase and increases cGMP level. NO synthase mRNA was detected in glomerulus and inner medulla. Soluble guanylate cyclase mRNA distributed widely along the nephron segments. NO and cGMP system seems to play some roles in modulating renal functions.