Infusion of L-arginine in experimental animals increases renal plasma flow (RPF) and glomerular filtration rate (GFR). It is likely that a component of these hemodynamic changes are mediated by nitric oxide (NO) as suggested by studies with specific antagonists of L-arginine metabolism. L-arginine administration ameliorates the infiltration of the renal parenchyma by macrophages in rats with obstructive nephropathy or rats with puromycin-induced nephrotic syndrome. L-arginine administration also blunts the increase in interstitial volume, collagen IV, and alpha-smooth muscle actin. Rats with a remnant kidney given 1% L-arginine in the drinking water had a greater GFR and RPF. L-arginine administration also decreased proteinuria. Diabetic rats given L-arginine had significantly lower excretion of protein and cyclic guanosine monophosphate than diabetic rats not receiving L-arginine. Despite persistent hyperglycemia, the administration of L-arginine prevented the development of hyperfiltration and ameliorated proteinuria in diabetic rats. In the setting of ischemic acute renal failure, the administration of L-arginine had a beneficial effect on GFR and RPF, decreased O2- production, diminished up-regulation of soluble guanylate cyclase, and prevented up-regulation of inducible NO synthase (iNOS). The pharmacokinetics of L-arginine indicate that side effects are rare and mostly mild and dose dependent.