In the view of the importance of esterified and free cholesterol in lipid metabolism, as well as serumtransaminase activity in the liver, the present study was designated to elucidate the effects of whole bodyX-irradiation on the levels of esterified cholesterol, free cholesterol and activity of serum transaminase inmouse. Also, in order to observe possible radioprotective action of reduced glutathione (GSH), a combination ofX-irradiation and injection of GSH was done to see tthe effects of GSH on lipid metabolism. A total of 132 micewere divided into four groups as ; Group I. 42 mice with whole body X-irradiation of 1,000r, Group II. 42 micewhich were injected with GSH(200mg/100gm Body Weight) prior to the X-irradiation, Group III. 42 mice which wereinjected with the same dose of GSH without the X-irradiation, and Group IV. The normal. Total and free cholesterolwere estimated by the method fo Zak and serum transaminase activity was studied by the method described byFrankel. The results obtained were summarized as follows; 1. The rate of cholesterol ester/total cholesterolshowed a tendency of gradual decrease by X-irradiation both in Group I and Group II with no significant differencebetween them. 2. The value of cholesterol ester/total cholesterol at 24 hours post-irradiation revealed the lowestin both Group I and Group II, and there were no noticeable differences between Grop III and the normal. 3. Serumtransaminase activities in all groups showed with in the normallimit, and there may have been no significantparenchymatous change in the liver.