An immunohistochemical study of basal cell adenoma of the major salivary glands was performed. All basal cell adenomas showed similar staining patterns. Carcinoembryonic antigen was expressed in the apical portions of luminal cells, in the luminal secretions, and in the duct-lining cells. Epithelial membrane antigen showed a similar pattern of expression but was less frequently present in duct-lining cells. Keratin expression was found in all epithelial cells but not in stromal cells. S-100 protein was strongly expressed in stromal cells, with focal positivity of cells in epithelial nests. Vimentin expression was noted in stromal cells and the outer layer of epithelial nests. Staining for muscle-specific actin was negative in both stromal cells and epithelial nests. Thus, there appears to be evidence of myoepithelial cell participation in the histogenesis of basal cell adenomas, and at least some basal cell adenomas appear to be closely related to pleomorphic adenomas.