BACKGROUND Very little information is available on the ultrastructure of the nasal cavity epithelium of the piglet. However, the nasal respiratory epithelium plays an important role in the pathology of atrophic rhintis of the piglet. Indeed, ciliated cells and mucus play a co-ordinate role in the colonization of the nasal cavity by the etiological agents of the disease. METHODS In the present study, samples of the ventral nasal turbinates of germ-free piglets were processed for observation in the transmission electron microcope to describe the ultrastructure of their covering respiratory epithelium. RESULTS Five morphologically distinct cell types were observed. Ciliated cells and basal cells were similar to that described in the nasal cavity of other species. On the basis of their secretory granule morphology, five forms of goblet cells were observed. Nonciliated, nonsecretory columnar cells with short, thick, regularly and densely spaced apical microvilli were identified as brush cells. A distinct type of secretory cells was found. Their apical surface protruded above the adjacent cells and had a few microvilli covered with thin hairlike projections. They were rich in smooth endoplasmic reticulum and had an apocrinelike type of secretion. CONCLUSIONS These findings indicate the complexity of cell types of the piglet nasal respiratory epithelium.