In patients with hepatocellular carcinoma and liver cirrhosis, complete removal of the portal unit containing the tumor is indicated because of portal invasion. Systematic subsegmentectomy achieves this goal in theory; however, the margin of the subsegment or segment in the liver parenchyma is unclear. To visualize the margin of the portal unit in the liver, we have invented a new method in which the portal pedicle is clasped and dye is injected. With this method, staining of the portal unit persists even after resection is complete, and the margin of the portal unit within the parenchyma is easily followed during transection.