An unusual case of pleomorphic adenoma displaying numerous horny pearls is described. The tumour arose in the right lateral lingual border of a 33-year-old man. In many pearls the cores were organized in two separate portions with distinct structural and histochemical features. The narrow peripheral portion had a compact structure and was rich in keratin since it contained cystine and was coloured with acid dyes of intermediate molecular size. The central portion was characterized by a loose texture and its histochemical profile (affinity for acid dyes of large molecular size, weak alcianophilia, vivid binding of colloidal iron) resulted from the existence of acidic mucosubstances in the cell coating of the neoplastic keratinized cells. These observations suggest that certain similarities exist between the processes of normal keratinization and squamous metaplasia in pleomorphic adenoma.