【Object ives】To analyse the local immunologic response in o ral squamous cell carcinoma (SCC) patients and investig ate the relationship betw een degree of tumor differentiation and immunoactivi ties by examining the phenoty pes of inf ilt rat ing lymphocy tes in situ .【Methods】16 patient s f rom 60 cases w ith o ral SCC

w hich w ere not given any preoperative t reatment

w ere selected .Frozen continuous slides

obtained f rom the surgical specimen of primary tumor

w ere analy zed immunohistochemically using the ABC method with monoclo nal antibodies (Anti-CD3 、CD4 、CD8 、CD16 and CD25).【Results】①All ty pes of lymphocy tes inf ilt rated in the tumor stroma

mostly located in the connecting zone betw een tumo r and normal tissue in clumps

sometimes in lymphatic follicles .② CD3 + 、CD4 + 、CD16 + and CD25 + cells had the same infilt rating pattern

but CD8 +

dif ferent f rom the others

usually scat tered into the cancer nest .③ The number of tumor-inf iltraling lymphocy tes w as associated w ith the deg ree of tumo r dif ferentiation .【Conclusion】Patients w ith oral SCC exist signif icant local immunologic response to tumor

but this activities was inhibited by tumor tissue .