Industrial glues contain many kinds of organic solvents and glue sniffing by young people has become a social problem in Korea. Glue vapor may induce chronic toxicities different from those induced by exposures to the solvent of single component. We studied the effects of the inhalation of glue vapor on the primary target organ, the pulmonary epithelium of the respiratory system. Vapor samples of glue were collected for analysis; the components were acetone, n-hexane, methyl cyclopentane, c-hexane, and toluene. For the inhalation of glue vapor, experimental mice were exposed in a whole body chamber for 20 min/d for 3, 5, 7, and 14 d. Control groups were exposed to room air. Animals were euthanized and lung tissues were fixed in 10% neutral formalin for light microscopy, and in 2.5% glutaraldehyde plus 1.5% paraformaldehyde for electron microscopy. The results are as follows. 1. Alcianophilic bands were not detected in the normal alveolar epithelium, but weak alcianophilic bands were detected in bronchioles. Alcian blue-PAS and PAS positive cells were found in the mucosae of mice exposed to glue vapor for 5 and 7 d. 2. Types I and II pneumocytes and capillary endothelial cells were found in the normal alveolar epithelium. The blood-air barrier consists of Type I pneumocytes, a common basal lamina, and the capillary endothelium. 3. The alveolar epithelium of vapor-exposed mice showed more type II pneumocytes. In the longerexposed group, Type I pneumocytes and endothelial cells contained many pinocytotic vesicles. 4. The vapor-exposed lungs showed macrophages in the alveolar space, mild interstitial swelling, and increased numbers of collagenous fibers. Clearly, ultrastructural changes in pulmonary epithelia can occur following glue sniffing.