SUMMARYBackground: Endothelins and nitric oxide regulate sinusoidal blood flow and the perfusion of the peribiliary vascular plexus. Aims: To study the serum and hepatic vein concentration of ET-1, ET-2, ET-3 and nitric oxide in patients with primary biliary cirrhosis and the effect of ursodeoxycholic acid treatment. Methods: Endothelins and nitrites/nitrates were measured in serum and hepatic vein blood in primary biliary cirrhosis and viral cirrhotic patients prior and after ursodeoxycholic acid therapy and in serum in controls. Endothelins were measured with commercial enzymelinked immunosorbent assays and nitrites/nitrates with a modification of Griess reaction. Results: The ET-1 and ET-3 levels were similar in patients and controls. Primary biliary cirrhosis patients