This article describes the preliminary findings of a Duplex ultrasound technique that enables the patency of the portal circulation and portosystemic shunt patency to be determined. In addition, the equipment allows the noninvasive measurement of quantitative rates of blood flow in these vessels. Portal vein flow was 952 +/- 273 ml/min in 10 normal subjects after an overnight fast and increased by 50% at 30 minutes in response to a standard 660-calorie liquid meal. Thirteen portosystemic shunts were scanned, and hemodynamic information was obtained from 10. Three of the four patients who had a Warren shunt performed 3 to 4 years earlier had portal vein occlusion. There is evidence of an increase in flow through the Warren shunt on feeding, suggesting a hemodynamic connection to the mesenteric side of the circulation. The apparatus, technique of examination, and the characteristics and difficulties with particular types of shunts are described.