BACKGROUND/AIMS: It is well recognized that all aerobic cells have the protective mechanisms in order to minimize the tissue damage induced by various reactive oxygen species(ROS). Thioredoxin peroxidase(TPX) which has been recently identified and characterized functions to convert peroxide to water. The protein is also found in various subtypes(TPX-A and B, MER5, HS22 and HORF-06) and is known to be ubiquitous in most human cells. Especially, ischemic brain injuries, partial hepatectomy and radiation induced DNA damages. In treating lung cancer, radiation therapy has a major place in the local control and the relief of symptoms, but radiation induced free radical injury and resulting pulmonary fibrosis has been the major drawback of the therapy. However, little is known about the protective mechanisms and biologic modulations against radiation induced tissue damages. METHODS: Eighteen mice were divided into six groups, 3 in each group, and fifteen had received 900cGy of radiation. The mice were sacrificed according to the pre determined time schedule; immediate, 1, 2, 3 and 6weeks after irradiation. Extracts were made from the lungs of each mice, Western blot analysis of various subtypes of TPX were done after SDS-PAGE. Examination of H and E stained slides from the same irradiated specimens and the control specimens were also performed. RESULTS: No difference in the intensity of the immunoreactive bands in the irradiated lung samples of the mice compared to the unirradiated control was observed regardless of the time intervals, although H and E examination of the sample specimens demonstrated progressive fibrotic changes of the irradiated lung samples. CONCLUSION: In conclusion, according to our data, it is suggested that various thioredoxin peroxidase subtypes and catalase which are known to be increased in many repair processes may not be involved in the repair of the radiation injury to the lung and subsequent fibrosis.