The metabolism and binding of the volatile halogenated hydrocarbon chlorobenzene-14C (CB) in the respiratory tract of mice was studied. As shown by whole-body autoradiography with heated tissue-sections, a selective localization of nonvolatile metabolites occurred in the mucosa of the entire respiratory system. Microautoradiography showed that tissue-bound metabolites were present in the epithelium of the nasal and tracheo-bronchial mucosa and in subepithelial glands in the olfactory nasal mucosa. In vitro experiments with slices from the nasal mucosa, lung and liver indicated transformation of CB to metabolites which could not be extracted from the tissues; the binding was most pronounced in the nasal mucosa. The formation of nonextractable metabolites by the nasal mucosa and lung in vitro was decreased by metyrapone, piperonylbutoxide and SKF 525, indicating a cytochrome P-450 dependent metabolism of CB in the respiratory tissues. Autoradiography of lung slices incubated with CB revealed that a preferential localization of metabolites in the bronchial mucosa also occurred in vitro. The results indicate that in situ metabolism of chlorobenzene in the mucosa of the respiratory tract may play a role in the pathogenesis of chlorobenzene induced bronchiolar necrosis in mice. The high binding of metabolites in the nasal mucosa suggest that this tissue may also be a site of toxic action of chlorobenzene.