A method for isolation and maintenance of the mouse lung ex vivo suitable for the study of the relationship between metabolism and toxicity is described. Physical, biochemical and morphological evaluations revealed that the lung is viable for up to 5 hr. No significant alterations in the architecture of the bronchiolar epithelium were observed by light or electron microscopy, despite evidence of interstitial and peribronchial edema. Although increases in pulmonary arterial pressure were noted at 5 hr, lung wet/dry weight was elevated only minimally (11%). Glutathione levels remained stable for the first 3 hr but fell to 57 +/- 14% of control at 5 hr. Naphthalene monooxygenase activity was not altered significantly during 5 hr of perfusion. Perfusion of the lung with naphthalene resulted in swelling and vacuolation of Clara cells followed by concentration-dependent losses of this cell type from the bronchiolar epithelium. Clara cells comprised 63% of the epithelial cells in terminal airways of control mice; 10 mumol of naphthalene decreased this number to 30%. Perfusion with naphthalene resulted in concentration-dependent decreases in pulmonary glutathione. Reactive metabolites were bound covalently to protein in the lung and in the perfusate. This study is the first to provide unambiguous evidence that naphthalene-induced Clara cell necrosis can be mediated entirely by processes resident in the lung. In addition, this work validates the use of the isolated perfused mouse lung for studying the role of reactive metabolites produced in situ vs. those entering the lung via the circulation.