Typical and atypical ultrastructural features of the cilia in the human nasal mucosa are reported in this paper. The specimens were taken from patients with the diagnosis of allergic rhinitis or chronic sinusitis. Most of the cilia showed a typical 9 + 2 arrangement of the axial filament complexes, but atypical axonemes such as 9 + 4, 8 + 2 and 10 + 2 patterns were found in six cilia of three patients. The supernumerary central fibrils were observed in one cilium only, whereas atypical patterns of the peripheral fibrils were found in five cilia. Cilia which contained a multiple axial filament complex, so-called compound clia, were also found in the mucosa of the chronic sinusitis cases. On the basis of their ultrastructural appearance, we classified these cilia into two groups, an "adhesive type" and a "bulging type." The former had a columnar shape of variable diameter, whereas the latter had a balloon-like form. The former contained closely packed multiple axial filament complexes whereas the latter possessed only sparse and irregularly oriented complexes. Electron-lucent lumina which were formed by the remnants of the ciliary membrane were frequently found in the former's transitional portion, but never in the latter.