Intrahepatic distribution of Lipiodol and I-131 Lipiodol infused via the hepatic arteries was evaluated in six patients with HCC who had undergone hepatic lobectomy or segmentectomy. CT scan and gamma camera radiograph confirmed that the oily contrast material or I-131 radioactivity accumulated selectively in the tumor over a long period. One to two thirds of the tumor mass appeared necrotic, although the extent tended to be larger in the case of radioactive Lipiodol infusion. The tumor cells contained numerous lipid globules within the cytoplasm. Also, oil red 0 stain demonstrated that the individual tumor cells had non-globular lipid on their surface. In conclusion, Lipiodol leaks out of the vascular spaces to attach to the cancer cell membrane as a non-globular lipid as well as to enter the cancer cells as a globular lipid. This phenomenon specific to cancer cells suggests a biochemical membrane change which may have occurred during carcinogenesis, causing alteration of membrane transport and cell death.