We have previously demonstrated that human olfactory epithelia can be classified into five grades according to the degree of degeneration present in patients with various kinds of olfactory disorders. In practice, however, the occurrence of additional types of cell changes in other kinds of olfactory disorders and findings with immunohistochemical techniques have led us to re-evaluate our previous classification. In the present study, changes in olfactory epithelia from ten patients with various kinds of olfactory disorders are discussed and a revised classification is proposed. Microvillar and differentiating cells were also evaluated in the epithelium studied.