Nonciliated bronchiolar epithelial (Clara) cells are selectively damaged by intraperitoneal administration of naphthalene. We examined these changes using light microscopy, transmission electron microscopy, and scanning electron microscopy. Naphthalene administration causes the Clara cells to expand and exfoliated shortly thereafter. Following exfoliation the remaining ciliated cells show morphologic abnormalities, including cilia loss and ballooning of remaining cilia. Upon regeneration of the Clara cells the ciliated cells gradually return to their normal appearance. One possible explanation for these findings is that the Clara cell secretions directly affect the physiologic state of the surrounding ciliated cells.