Studies performed over the last 10 years have evaluated the role of nitric oxide (NO) in the control of renal hemodynamics. This article reviews the effects of administration of nitric oxide synthase (NOS) blockers on renal function in experimental animals and human volunteers. These studies show that NOS blockade increases renal vascular resistances and decreases the glomerular ultrafiltration coefficient. These experimental studies also support the presence of an important interaction between NO, angiotensin II, and renal nerves in the control of renal function. The use of acute and chronic administration of NOS blockers has generated a great deal of new and exciting information regarding the role of NO in the regulation of normal renal function.