Serial changes of intrahepatic portal blood flow were studied before and after percutaneous ethanol injection therapy (PEIT) for hepatocellular carcinoma (HCC). In all eight patients examined, wedge-shaped perfusion defects distal to the tumor were clearly demonstrated by dynamic sequential computed tomography during arterial portography (CT-AP). However, no abnormalities of arterial blood flow were detected in the areas of reduced portal blood flow by enhanced computed tomography (CT), indicating that portal blood flow of the liver was selectively decreased by PEIT. Moreover, histopathological finding of two resected liver tissues after PEIT revealed organized thrombi in the portal veins in the non-cancerous liver tissues distal to the tumors. These findings suggest that decreased segmental portal flow is frequent after PEIT and obstructive vasculitis is caused by the drainage of ethanol injected in the tumor.