1-131-Lipiodol, a new therapeutic agent, has been used in the tratment of hepatocellular carcinoma(HCC) since Lipiodol retains within the vascular HCC following intrahepatic arterial injection. Radioiodination of Lipiodolwas achieved by using a simple exchange method and the agent was used for the tratment of HCC following the biodistribution studies in dogs and human subjects. Desired radiation doses can easily be delivered upto 12,000rad while keeping the radiation doses to normal liver, lung and whole body safe and tolerable. Clinical studies in50 patients with hepatoma were performed by this method in order to estimate the therapeutic effect, safety,indication and limitations, The results as follows: 1. Biodistribution studies The effective half life of1-131-Lipiodol in the tumor was 6 days and retained in the tumor as long as 3 months. About 10% of radioactivity was demonstrated in the lungs with effective half life decay. The 1-131-Lipiodol in the normal liver tissue seemsto be metabolized in the hepatocytes and excreted into the bile and urine. No demonstrable radioactivity was notedin the thyroid, bowels, spleen and bone marrow. 2. Histologic studies Histologic studies following the intrahepatic 1-131-Lipiodol of the canine liver revealed the Lipiodol particles in the bile duct cells andcytoplasm of hepatocytes. In human resected hepatomas after 1-131-Lipiodol infusion, Lipiodol drophlets were demonstrated in the tumor vessels, sinusoids as well as in the tumor cell cytoplasm, Extensive hemorrhagicnecrosis of tumor was demonstrated after treatment with 1-131-Lipiodol. 3. Clinical studies Response rate was mostprominent in those cases of single massive types which measures less than 5cm in diameter. Multinodular type was also responsive rather than single massive type, however, infiltrative type of tumor or the tumors measuring morethan 8cm was less effective on this therapy. 4. Adverse reactions Adverse reactions from the procedure includefever abdominal pain and elevation of liver function which were mild and tolerated well. There were no sideeffects suggestive of bone marrow depression or lung complications. In conclusion, 1-131-Lipiodol is a promising agent for the treatment of hepatoma less than 8cm in size by simple or multiple procedures diverling high internal radiation dose to the tumor without any bone marrow depression, lung complications or radiation hepatitis.