Biopsied specimens from 55 patients with squamous cell carcinoma (SCC) of the oral cavity were examined immunohistopathologically as to the clinical significance of basement membrane (BM) deposition and T-cell infiltration at the tumorstromal border using monoclonal anti-laminin and anti-CD3 antibodies. According to the immunoreactivity, all specimens could be divided into three groups: group A, a continuous linear pattern of positive staining for BM around tumor nests; group B, an alteration of BM deposition around tumor nests with T cell infiltration into those tumor nests; and group C, an alteration of BM deposition around tumor nests without T cell infiltration into those tumor nests. These groups were correlated with clinical manifestations, such as tumor size, tumor regression rate with induction chemotherapy, and regional lymph node metastatic rate. In these groups, tumors classified as group C showed a trend toward resistance to chemotherapy and high metastatic characteristics. Tumors classified as group B, which showed the same alteration of BM deposition as a result of T cell infiltration into the tumor nests, showed a sufficient tumor regression rate with chemotherapy. The visualization of the staining for BM laminin and T cells in oral SCC appeared not only to increase our understanding of the biologic and clinical behavior of individual tumors, but could be a prognostic indicator.