C(57)-Black female mi^e were divided into the next 7 groups for the purpose of examining the effects of the exhaustive physical exercise before and after the irradiation. Group 1. Exercised for 30 minutes directly before the irradiation (RE pre-30 m.) Group 2. Exercised for 1 hour directly before the irradiation (RE pre-1h)Group 3. Exercised for 2 hours directly before the irradiation (RE pre-2h) Group 4. Exercised for 1 hour after the irradiation (RE post) This exercise was continued for 30 days at the rate of 1 hour per day and 6 days per week after irradiation. Group 5. Exercised control (EC) This exercise was the similar as that in Group 4 Group 6. Radiated control (RC) Group 7. "Thyradin" injected (TR) "Thyradin" (thyroid preparation) was injected 0.2 c. c. (contains 10γ of iodine) per 10 grams of body weight, and then the animals were exposed to X-ray on the 7th day after irradiation. Exercised groups were made to run in the cylindrical tread-mill (80 cm in circumference, 8 rotations per minute, i.e. the animals have to run at a speed of 6.4 m per minute). Irradiated groups received 600 r, 660 r and 840 r of X-ray at 99 r per minute. Gas analyses were done in order to evaluate the metabolic level of the exercise on one mouse in each group which was made to run in another tread-mill of the same diameter, rotating in the same speed as one described above, and located in an air-tight chamber shown in fig. 1. The air sample from this chamber was analysed with Scholander's apparatus. This results are as follows: 1) The metabolism increased by the exercise showing 33.85 % (mean) increased of the oxygen consumption. 2) The metabolism was accelerated gradually by the "Thyradin" treatment arriving the maximum arround the 6th day after the injection, showing 42.99 % of the increase of oxygen consumption. 3) The survival rate in the groups which were exercised before the irradiation was higher than that in the group of radiated control and the group exercised after the irradiation. The difference of the survival rate detween the groups exercised bafore the irradiation and the groups exercised after the irradiation was significant (P<0.05). 4) The survival rate in the groups which were exercised before the irradiation was not in proportion to the quantity of the exercise before the irradiation. 5) The metabolism was increased by the injection of "Thyradin" and lowered the survival rate. 6) The weight in the group of radiated control dropped down day by day, but in the group exercised before the irradiation began to recover after three weeks of irradiation. 7) The weight in the group injected "Thyradin" decrease extremely 2 weeks after the irradiation.