The author investigated the effect of the radioactive thermal bath upon the carbohydrate metabolism and the leucocyte picture in alloxan-diabetic rabbits. 1. The author injected 100-200 mg. of alloxan per kg. of body weight intravenously into normal rabbits and produced alloxan diabetes. The triphasic blood sugar response to the injection of alloxan is illustrated in Table 1. and Fig. 1. About a week after the injection of alloxan, the fasting blood sugar values ranged 127 to 331 mg./dl. (Table 3.). 2. In this experiment the alloxan-diabetic rabbits were put in radioactive hot spring and plain water bath, 42-44℃. in temperature. The radioactive hot springs put in use are "Hisui-no-Yu" and "Kenkyusho-sen" (the Loboratory-Spring), both in Misasa Spa, the chemical compositions of which are given in Table 2. 3. In any case, the blood sugar level rose temporarily after the thermal baths for 5 minutes, but the 24-hour blood sugar value after taking a bath was lower in "Hisui-no-Yu" (Rn: 300-400 Mache units) than in "Kenkyusho-sen" (Rn: 10-30 Mache units) (Table 3 and Fig. 2). 4. The glucose tolerance was found to be abnormal in alloxan-diabetic rabbits even 3 months after the injection of alloxan, but this abnormal carbohydrate metabolism tended to become normal by the radioactive thermal bath (Table 5, 6 and Fig. 3, 5.). 5. The radioactive thermal bath in "Hisui-no-Yu" caused increase of leucocyte counts of alloxan-diabetic rabbits more remarkably than the bath in "Kenkyusho-sen" (Table 8. and Fig. 6).