Variant expressions of modified myoepithelial cells in salivary pleomorphic adenomas are described as determined by immunohistochemical techniques which visualized the distributions of S-100 protein, intermediate-sized filament proteins (keratin, vimentin, and desmin), and contractile proteins (myosin and actin), as well as lysozyme and lactoferrin. Immunohistochemical staining patterns of S-100 protein were basically used to classify modified myoepithelial cells, along with histologic criteria. Histochemical modifications of myoepithelial cells in pleomorphic adenoma of salivary glands could be divided into a) reactive, b) transformed, and c) neoplastic myoepithelial cells. Reactive myoepithelial cells were stromal-like cells which displayed an intense S-100 protein reaction. Transformed myoepithelial cells were negative or slightly positive for S-100 protein; they were located in the outer zone of tubular or duct-like structures and were spindle-shaped. The inner round cells of tubular and ductal structures, which could be ductal origin, gave intense keratin staining, as well as marked reactions for lysozyme and lactoferrin. Neoplastic myoepithelial cells were plasmatoid or fibrous types of cells and contained abundant S-100 protein and vimentin. These cells were termed "myoepithelioma" as in classical diagnosis.