The functional role of Langerhans cells (LCs) in oral cancer was studied, based on a quantitative analysis of LCs in squamous cell carcinomas arising from the tongue. LCs were identified by their positiveness for S100-protein and other cytological characters based on PAP method. LCs increased in number in the cancer region and showed an intimate relationship with lymphocytes in terms of their number and distribution. Moreover, in those cases with many LCs, clusters consisting of LCs and lymphocytes were often found to combine into "hydropic degeneration-like" lesions as seen in allergic disease such as dermal lichen planus. These findings, as well as the review of literature, suggested some immunological role of LCs in oral carcinoma.