Abstract: Objective To investigate the effects of a combination of interstitial implantation of an ¹²⁵I seed with 5-FU on growth and pathological changes of hepatocarcinoma cell line H22. Methods A total of 40 KM mice were transplanted subcutaneously with H22 cells.Tumor-bearing mice were then divided randomly into 4 groups（each n = 10）.An ¹²⁵I seed and 5-FU were embedded into the tumor of each mouse in group A；mice in groups B and C were treated，respectively， with an ¹²⁵I seed or 5-FU；mice in group D did not receive any treatment.All animals were sacrificed 28 days later；survival rate and tumor size were measured，and tissue samples were analyzed by routine histopathology and electron microscopy. Results Mean tumor volumes in each group were as follows：group A，1.38±0.11 cm³；group B，2.11±0.19 cm³；group C，2.79±0.23 cm³；group D，4.34±0.29 cm³.Volumes were significantly different a-mong the groups （P<0.01）. The extent of tumor volume inhibition was 68.21% in group A， 51.38% in group B and 35.71% in group C. Histopathological observation showed that the major change in group A was cell necrosis， while samples from groups B and C showed scattered necrotic cancer cells，with a large number of lymphocytes around. Electron microscopy of group A samples showed complete or incomplete necrosis and sometimes apoptosis of cancer cells，while samples from groups B and C showed most tumor cells to have an integrated nuclear membrane，dense chromatin and numerous cytoplasmic protuberances or chromatolysis and apoptotic bodies.Samples from these two groups also showed numerous aggregated apoptotic cancer cells. Conclusion ¹²⁵I seed interstitial im-plantation can promote apoptosis in H22 cells.Use of an ¹²⁵I seed combined with 5-FU interstitial chemotherapy can further promote tumor cell degeneration， necrosis and apoptosis.The combination of ¹²⁵I and 5-FU has synergistic effects，providing a new option for treating liver cancer.

Key words: ¹²⁵I seed, Liver neoplasms, Apoptosis, Cell growth, Pathologic changes