Tenascin is a multifunctional extracellular matrix glycoprotein generally expressed in epithelial tumors at sites of epithelial tumor-mesenchymal tissue interface. Studies so far have indicated that mesenchymal cells are a major source of tenascin in tumor tissues. The present study evaluated biopsies and surgically resected specimens of oral squamous cell carcinoma from 20 patients for the expression of tenascin using immunohistochemical methods. The normal mucosa included in all surgically resected specimens showed a delicate band in the submucosal connective tissue, with infrequent breaks in continuity in the immediate vicinity of the basement membrane. The hyperplastic/hyperkeratinized or dysplastic mucosa either showed a continuous band or enhanced expression of TN in the submucosal connective tissue. Evaluation of serial sections for immunoreactivity of tenascin in 7 cases of carcinoma showed intracellular localization of tenascin; particularly at the invading fronts of carcinomas of the buccal mucosa and tongue. The results of the present study may imply that despite the possible induction of tenascinllfrom mesenchymal cells by carcinoma cells, carcinoma cells, if they produce tenascin, do so at the invasive fronts.