Rats were kept for 4 weeks on a dietary regimen with a low or high sodium intake to increase or reduce, respectively, the renin activity of the kidneys and plasma. Fibrinolysis was inhibited by intravenous injection of AMCA and thrombin was infused into the jugular vein, giving rise to heavy intravascular fibrin deposition in the kidneys. Shortly after the thrombin infusion the glomerular filtration rate (GFR) decreased equally in saline-loaded and normal rats. 48 h after the thrombin infusion the GFR was still markedly reduced in saline-deprived and normal rats but had returned to preinfusion values in the saline-loaded rats. The results might indicate that the renin-angiotensin system is involved in the persistence of the renal functional impairment after intravascular coagulation in the rat kidney.