The ultrastructural characteristics of the hairlike variations of filiform papillae in the human tongue were studied by scanning and transmission electron microscopy. The scanning electron microscope gives evidence of a three-dimensional image of abnormally long secondary papillae with the epithelial cells arranged like roof tiles. These are partly adhering, partly detached, and then protruding from the core, thus forming the hairlike structure. Transmission electron microscopy of ultrathin sections shows single or partly adhering, orthokeratinized epithelial surface cells, mostly with distinct signs of degradation, surrounded by microorganisms. The pathomorphologic picture of elongated, hairlike filiform papillae was observed on the tongue coating of patients with clinically diagnosed hairy tongue but also on some small areas of the tongue of infants. These latter findings cannot be characterized by the clinical term "hairy tongue" but must be considered to be hairlike variations of filiform papillae.