Azygos venous blood flow estimated by the continuous thermodilution method was measured in 48 patients with portal hypertension. In patients with cirrhosis, azygos venous blood flow was 326 +/- 139ml/min (mean SD) and was significantly higher than in patients without portal hypertension (163 +/- 61ml/min). In patients with idiopathic portal hypertension and extrahepatic portal obstruction, azygos venous blood flow was 411 +/- 227ml/min and 328 +/- 85ml/min respectively. Azygos venous blood flow was significantly correlated with the hepatic venous pressure gradient but neither with cardiac output nor with size of esophageal varices. In eleven cirrhotic patients, azygos venous blood flow and other hemodynamic parameters were measured before and after the nonshunting operation of esophageal transection, splenectomy and esophagogastric devascularization. Azygos venous blood flow and hepatic venous pressure gradient were significantly reduced after operation. On the other hand, cardiac output did not change significantly after surgical procedure. Relatively high postoperative azygos venous blood flow indicates its important role in the postoperative collateral circulation.