A method to quantitate blood flow through the gastroesophageal collaterals in portal hypertensive patients was developed. Since gastroesophageal collaterals drain into the azygos system, it is postulated that measurement of blood flow in the azygos vein should provide a quantitative measurement of gastroesophageal collateral blood flow changes in portal hypertensive patients. Azygos blood flow was measured using a double thermodilution catheter directed under fluoroscopy to the azygos vein. Ten patients with alcoholic cirrhosis were studied. Five of these patients had a history of repeated bleeding from gastroesophageal varices (Group I). The azygos blood flow in these patients was 596 +/- 78 ml per min. The other five patients all had decompressive surgery of the portal system (Group II). In these patients the azygos venous blood flow was 305 +/- 29 ml per min (p less than 0.01). The coefficient of variation of repeated baseline measurements was of 4.4 +/- 0.6%. The azygos venous blood flow measurement is a rapid, simple and sensitive method to evaluate blood flow changes in the vessels involved in gastroesophageal bleeding due to portal hypertension.