Nitric oxide (NO) is a gaseous free radical and an important molecular mediator of many physiologic processes in virtually every organ. NO is produced from L-arginine by nitric oxide synthase (NOS). This enzyme is expressed as 3 isoforms, all of which have been isolated from the kidney: endothelial NOS (eNOS), neuronal NOS (nNOS), and inducible NOS (iNOS). At present it is very difficult to measure authentic nitric oxide in vivo; a way to circumvent the difficulties is to study the effects of NOS stimulation and subsequent nitric oxide release directly by measurement of the resulting changes in vascular tone. In the kidney and vasculature, NO plays fundamental roles in the control of systemic and intrarenal hemodynamics, the tubuloglomerular feedback response, pressure natriuresis, release of sympathetic neurotransmitters and renin, and tubular solute and water transport. Chronic renal failure (CRF) is a state of NO deficiency secondary to decreased NO production and/or increased bioinactivation of NO by reactive oxygen species. The purpose of this review is to examine the functions of NO in the kidney, and to discuss the effects of NO deficiency in the progression of chronic kidney disease.