Four cases of basal cell adenoma of the parotid gland were examined immunohistochemically to characterize their cellular composition. In all cases epithelial membrane antigen and keratin were detected in the inner luminal cells; some cells also showed positive staining for secretory functional markers, indicating their differentiation toward secretory epithelium. In tubular and trabecular types the outer cells consistently displayed an intense staining for vimentin and some were also positive for actin, indicating their myoepithelial nature. In the solid type, most tumor cells resembled the ductal cells or basal cells of larger ducts in normal gland with regard to their immunoreactivity. Our results may suggest that the proportion and arrangement of heterogeneous tumor cells are responsible for different histologic patterns of the salivary basal cell adenoma.