Portal hemodynamics were studied in 55 patients with hepatocellular carcinoma in comparison with 41 normal subjects, using the duplex system that consists of an electronic sector scanner and a pulsed Doppler velocitometer. Changes of portal hemodynamics after transcatheter hepatic artery embolization were also investigated in 15 of the patients with hepatocellular carcinoma. The duplex system showed that 9 of the 55 had no Doppler signal in the portal trunk, suggesting portal vein thrombosis, 2 had hepatofugal flow in the portal trunk indicative of arterioportal shunts, and 44 had hepatopetal flow in the portal trunk. One of the 9 patients with no significant portal venous flow showed hepatopetal flow in collateral veins at the porta hepatis, suggesting cavernous transformation of the portal vein. All of these ultrasound findings were confirmed by subsequent celiac-mesenteric angiography. In 44 of the 55 patients there was no tumor invasion in the portal trunk, and portal venous flow was found to be close to that of normal subjects regardless of the stage or size of tumor, and tumor invasion into relatively large portal branches. After transcatheter hepatic artery embolization, portal venous flow was increased, even on the next day, and it remained increased for at least 2 wk. Thus, the duplex system is useful to study qualitative and quantitative changes of portal hemodynamics in hepatocellular carcinoma. Our observations suggest that the portal venous flow is kept relatively constant by some homeostatic mechanism even in advanced hepatocellular carcinoma until the tumor invades into the portal trunk, and that it increases when hepatic arterial flow is occluded.