In Order to investigate the features of the response of Various tissues to radiation-induced lipoperoxidation stress, the SeGsHpx activity in RBC, plasma, liver, Spleen and small intestine of mice irradiated with various doses (500, 1000 and 2000 rad)and at various intervals after irradiation was determinated. The results showed that the forms of the response of Various tissues to radiation-induced lipoperoxidation were different from each other and might be grouped under four heads: 1) The tissues such as mature RBC, which cannot synthesize SeGSHPx. The characteristic change was that the enzyme activity decreased after irradiation; the extent of inhibition was increased with the increase of irradiation dasage, and became higher as time elapsed after irradiation with large dose (2000 rad). 2) non radiation sensitive tissues such as liver, which can synthesize SeGSHPx. It can response to radiation induced lipoperoxidation stress, but when the irradiation dosage was large enough to damage liver cells, the increase in the enzyme activity became less, in severe damage (2000 rad), SeGSHPx activity was decreased on the contrary; 3) Radiationsensitive tissues such as spleen. Owing to the necrosis of most spleen cells, the measured SeGSHPx activity could not entirely reflect that of lymphocytes and was thought to be influenced by the relative content of reticular cells in the spleen. In the sensitive tissue of small intestine, when irradiation dose was 2000 rad, as the intestinal mucosa was extensively detached the enzgme activity was decreased. But when the sensitive tissue that was damaged (1000 rad) reProduced again, the SeGSHPx activity could present an increase; 4) The enzyme activity in plasma was primarily decreased but it would become higher at some time after irradiation. This increase was mainly based on the release of SeGSHPx into blood from the destoyed spleen cells.