Objective: To investigate the effect of mouse hepatocarcinoma cell line HCa-F (high metastatic potential) and HCa-P (low metastatic potential) on immune system of the host. Methods: Mice were subcutaneously implanted with HCA-F (F) or HCa-P (P) cells. Cell cycle of lymphocytes from metastatic lymph nodes of tumor-bearing mice was studied by flow cytometry. Fas-L expression of F and P cells was detected immunohistochemically. Apoptosis of macrophages in metastatic lymph nodes was examined by TUNEL methods. Results: For the Hca-F cell bearing mice, the proliferating peak of lymphocytes appeared on 14th day post-inoculation and then decreased rapidly, while for the Hca-P cell bearing mice, the peak appeared on the 7th day post-inoculation and then kept at high level. The expression of Fas-L in F cells was stronger than that in P cells (P<0.01). Apoptosis occurred in macrophages near metastatic F cells in lymph nodes of tumor-bearing mice. Conclusion: Carcinoma cells with high metastatic potential may suppress immune reaction of host through inducing apoptosis of macrophages (one of the important antigen present cells) by Fas-L-Fas interreaction. And the expression of Fas-L in tumor cells may be associated with high metastatic ability to lymph nodes. Objective: To investigate the effect of mouse hepatocarcinoma cell line HCa-F (high metastatic potential) and HCa-P (low metastatic potential) on immune system of the host. Methods: Mice were subcutaneously implanted with HCA-F (F) or HCa -P (P) cells. Cell cycle of lymphocytes from metastatic lymph nodes of tumor-bearing mice was studied by flow cytometry. Fas-L expression of F and P cells was detected immunohistochemically. Apoptosis of macrophages in metastatic lymph nodes was examined by TUNEL methods. Results: For the Hca-F cell bearing mice, the proliferating peak of lymphocytes appeared on 14th day post-inoculation and then decreased rapidly, while for the Hca-P cell bearing mice, the peak appeared on the 7th day post-inoculation and then kept at high level. The expression of Fas-L in F cells was stronger than that in P cells (P <0.01). Apoptosis occurred in macrophages near metastatic F cells in lymph nodes of tumor-bearing mice. with high metastat ic potential may suppress immune reaction of host through inducing apoptosis of macrophages (one of the important antigen present cells) by Fas-L-Fas interreaction. And the expression of Fas-L in tumor cells may be associated with high metastatic ability to lymph nodes .