Objectives: Salivary gland tumors pose considerable difficulty in diagnostic and prognostic assessment based on the histopathologic features alone. We studied the expression of type IV collagen and fibronectin in salivary gland tumors with special emphasis on the differential diagnostic significance. Materials and Methods: We did immunohistochemical stain on paraffin embedded tissues of 33 benign and 24 malignant salivary gland tumors using monoclonal antibody for type IV collagen and polyclonal antibody for fibronectin. Results: 1) Well preserved linear basement membrane-like staining of type IV collagen was detected in duct-cell-derived benign salivary gland tumors. But pleomorphic adenoma exhibited a heterogeneous pattern as focal augmentation and interruption. 2) In malignant tumors, type IV collagen was distributed in an irregular, interrupted manner or completely absent. Adenoid cystic carcinomas displayed a marked staining of the basal membrane associated substances in the pseudocysts. 3) The staining pattern of fibronectin was similar to that of type IV collagen execpt more dense in the stroma. 4) Salivary gland tumors which have a prominent myoepithelial cell component revealed a particular deposition of basement membrane materials adjacent to the myoepithelial cells. Conclusion: The study of the basal membrane substances may be helpful for differential diagnosis of benign and malignant salivary gland tumors and identifying special features of salivary gland tumors such as pseudocystic pattern of adenoid cystic carcinoma. Also we think that the myoepithelial cells contribute to the formation of basement membrane materials.