In order to see the utilization of B(1)-intake under a hot and highly humid environment, the author raised albino rats under a hot and highly humid environment keeping the hygrometric temperature around 28-30°C and administering B(1), stimated the tissue B(1)-content, changes in the body weignt, the amount of food consumed, and the B(1)-content excreted in the urine. The following are the results. 1. When the daily dose of 6γ B(1) was adminstered for one week to albino rats raised with B1-deficient Shimazono diet under a hot environment. the B(1)-concentration of the heart was 1.3 times that of the control raised under the normal environment, and the B(1)-concentration in the liver, kidneys, and brain was likewise somewhat higher but the B(1)-content was smaller than that in the control. 2. When the daily dose of 40γ B(1) was given one week to the albino rats raised with the B(1)-defieient Shimazono diet, the tissne B(1)-concentration was rather higher in the heart and kidneys than in the control, but the B(1)-content was lower in the liver and no differences could be observed in other tissues as compared with the control. 3. After injectiog 0.5r/g B(1) to the albino rats raised with B1-deficient diet under the hot environment and by bathing in hot water for 10 minutes every one honr the concentration of tissne B(1) after 9 hours showed no difference from that in the control, but the B(1)-content was generally lower, especially the B(1)-content in the heart and liver was only about 60-70 per cent of the control. 4. The B(1)-content excreted in the urine of the albino rats raised uuder a hot environment in the case of daily administration of B(1) under the dosc of 6γ showed no difference from that in the control raised under the normal temperature, but when the daily dos of B(1) was raised to 40γ or 80γ, the B(1)-content excreted in the urine at last rose to 1.3 times that on the control.