To study the effect of hog cholera virus on the epithelial cells of the bronchiolar mucosa, 12 pigs were inoculated with a highly virulent strain. Immunohistochemical and ultrastructural examination of the ciliated epithelial cells demonstrated an increase in the number of atypical cilia. The latter showed alterations in the microtubular pattern. possibly resulting from viral interference with the normal metabolism of the epithelial cells. (C) 2001 Harcourt Publishers Ltd.