Renal endothelin (ET) production was investigated in rats after renal mass ablation, a model of progressive renal disease characterized by glomerular hemodynamic alterations and capillary thrombosis, and in sham-operated animals. Thrombin stimulation of renal cortical tissue from rats with renal mass reduction, 45 but not 7 days after surgery, generated significantly (P less than 0.01) more ET than tissue from sham-operated animals. Exposure to thrombin of isolated glomeruli from remnant but not sham kidneys also significantly (P less than 0.01) increased ET production compared with unstimulated glomeruli. At day 45, in rats with renal mass ablation ET plasma levels were numerically lower, whereas urinary excretion rate of ET was significantly (P less than 0.01) increased compared with sham-operated animals. After a 50-min intravenous infusion of 125I-ET to normal rats and animals with renal mass ablation, less than 0.3% and 0.03%, respectively, of total infused radioactivity was recovered in urine. These results indicate that thrombin-stimulated ET production by renal cortical tissues is increased in rats with renal mass reduction. Despite normal or low-normal plasma ET levels, urinary excretion of the peptide is markedly increased in this model. The exogenously labeled ET added to circulation is not excreted by the kidney, suggesting that enhanced urinary excretion rate would reflect an increased renal production of the peptide in rats with remnant kidney.