We examined the effects of trichloroethylene (TCE) on the bronchiolar epithelium of mouse lung, using scanning electron microscopy. The lesion elicited by TCE involved predominantly the nonciliated Clara cells of the bronchiolar epithelium. Although there was slight loss of cilia and the mucosal surface exhibited increased deposits of debris throughout the period the tissues were observed, the ciliated cells appeared relatively uninjured. At 24 h following the intraperitoneal administration of TCE (2000 mg/kg) the Clara cells of the bronchiolar epithelium were irregularly distributed on the mucosal surface and reduced in number, indicating loss of cells by exfoliation. The remaining Clara cells appeared deformed and collapsed. This cell population was markedly reduced by seven days after TCE exposure, and the bulging apices characteristic of this cell type were virtually absent, resulting in a flattened epithelial lining. By 15 and 30 days after TCE, reparative processes were evident and micronodules consisting of multiple Clara cells protruded into the airway lumen. The administration of TCE to mice causes severe morphological damage to Clara cells of the bronchiolar epithelium which persists for at least 60 days after chemical exposure.