Abstract: The purpose of this study was to determine the effect of ammonia gas for respiratory organs of rats at various concentrations and exposure duration. Meanwhile, the exposure conditions were evaluated when isolators were used as the inhalation exposure equipments. 120 rats were divided into five groups randomly. One group was used as control and the others were exposed to ammonia at 10, 20，40 and 170 ppm respectively. The respiratory organs were sampled for histopathological study on 30，55， and 108 days post exposure. The result showed that histopathological changcs were found in rats that had been exposed to 170 ppm NH3 after 30 days, such as severe loss of cilia， squamous metaplasia, ulceration and necrosis with variable inflammation of the subepithelial tissue in upper respiratory tract, exudate in the nasal passage. Noticeable lesion in upper respiratory tract，especially in nasal cavity, were seen in rats exposed to ammonia at 20 ppm for 108 days. No changes were found in other examinations at this concentration. When the ammonia concentration was 10 ppm, no effects were observed in rats exposed for 108 days. Therefore, the effects of ammonia at 20 ppm and histopathological changes in the nasal of rats was the most sensitive indicator for ammonia at low concentration.

Key words: Ammonia, Respiratory Organs of Rats, Histopathology