Objective To investigate the expression of tumor necrosis factor alpha(TNF-α)and its relationship with infiltrating lymphocytes in lichen planus(LP).Methods Tissue specimens were obtained from the lesions of 60 patients with LP and normal skin of 20 human controls.Immunohistochemical SP method was used to detect the expression of TNF-α,and infiltrating lymphocytes were counted in TNF-α-positive tissue sections.Results TNF-α was expressed in 72％ of the LP specimens but in none of the control specimens(P ＜ 0.01).Positive staining for TNF-α was mainly located in the membrane of prickle cells,cytoplasm or membrane of dermal infiltrating lymphocytes.The expression of TNF-α in LP was uncorrelated with age,sex or disease course(all P ＞ 0.05),but was positively correlated with infiltrating lymphocyte number (rs =0.47,P ＜ 0.01).Conclusion TNF-α seems to play a certain role in the pathogenesis of LP.