OBJECTIVE To investigate perforin and Fas-ligand (Fas-L) expression of tumor infiltrating lymphocytes (TIL) in human hepatocellular carcinoma (HCC). METHODS Expression of perforin and Fas-L of TIL was studied in 20 HCC cases using in situ hybridization and immunohistochemistry. RESULTS Expression of perforin and Fas-L gene were detected in TIL in 80% of the cases studied. Among them, one patient (no. 14) in whom expression of perforin and Fas-L were noticed in the majority of the TIL, had no recurrence of HCC for one and one half (1.5) year after tumor resection. It indicates that presence of large number of activated T cells might be beneficial for the tumor therapy. In the remaining cases, only 10% of TIL were obtained able to express perforin and Fas-L indicating that only a few TIL were activated and cytotoxic to HCC. CONCLUSIONS Even there were a multitude of T cells infiltrating in HCC, only few of them were immunoactived and to be cytotoxic to HCC. It seems important to adopt measures in order to promote further proliferation of these activated T cells either in vitro or in vivo.