To determine the pathological behavior of human hepatocarcinoma cells in the liver microenvironment of neonatal non-immunode-ficient mice, three human hepatocarcinoma cell lines (Be7402, HepG2, and SK-Hep-1), traced by Dil, were transplanted into the intrahepatic or subcutaneous tissue of neonatal and adult Kunming mice. Histopathological observations showed that cells in the adult liver induced a severe immune response as early as the second day after the implantation, while the subcutaneous neoplasm underwent extensive necrosis by the end of the study. Only the cells injected into the neonatal liver underwent a delayed immunologic rejection in the organ mieroenvironment. These cells retained recognizable tumor features over the first seven days, and displayed an intrahepatic inva-sive pattern. The expression of tumor markers including alpha-fetoprotein and survivin was maintained. The quantitative ELISA for the expression patterns of IL-2 and IL-10 also confirmed that the intrahepatic immunity was non-susceptive during this period. The high serum alpha-fetoprotein level was inversely correlated with the change in immune response. Our study provided a bio-system for the research of immune responses to xenografts in the liver.