Monoclonal antibody for keratin K8.12 (keratin nos. 13 and 16) was evaluated in paraffin sections of 17 cases of obstructive sialadenitis and 97 pleomorphic adenomas. In normal salivary glands fixed with 10% formalin, K8.12 staining was strongly limited to ductal basal cells, and staining to PKK1 and KL1 was positive in duct cells. Monoclonal antibodies PKK1 and KL1 were compared in duct-like structures of obstructive lesions and pleomorphic adenomas. Duct-like structures in obstructive lesions showed strong staining for K8.12 in ductal basal cells, and positive staining for PKK1 and KL1 in ductal epithelial cells, in different stages of ductal obstruction. Pleomorphic adenomas showed an intense expression for K8.12 staining in outer tumor cells of tubulo-ductal structures, and positive reaction for PKK1 and KL1 in luminal tumor cells. The histogenesis of pleomorphic adenoma is discussed in terms of the immunohistochemical labelling of the 3 types of monoclonal antibodies to keratin. The identification of a progenitor cell to ductal basal cells is also hypothesized.