We measured plasma concentration of endothelin-1 in three children with Byler's disease, five with biliary atresia after portoenterostomy, and nine controls. No patients had ascites or hepatorenal syndrome. Plasma endothelin-1 levels were significantly higher in patients with Byler's disease than in the controls (5.19 +/- 0.90 versus 1.81 +/- 0.19 pg/ml, respectively; p < 0.01), but were normal in operated biliary atresia. Urinary concentrations of N-acetyl-beta-D-glucosaminidase (NAG) were significantly higher in the patients with Byler's disease than in controls. Plasma endothelin-1 level correlated significantly with serum concentration of bile acid (r = 0.91; p < 0.01) and urinary concentration of NAG (r = 0.92; p < 0.01). We conclude that plasma endothelin-1 levels are high in patients with severe biliary cirrhosis and that endothelin-1 may partially contribute to development of renal injury in cirrhosis.