By estimating the contents of pyramin and vitamin B(1) excreted in the urine of the albino rats raised under the hot and highly humid environment of hygrometric temperature at 28-30°C, the author obtained the following results. 1. When the daily dose of 40γ B(1) was administered to the albino rats being raised under a hot environment, the mean averago of the pyramin content excreted in the urine per day by an individual rat was around 3.52-3.38γ, showing no difference from that of the control. While the B(1)-quantity excreted in the ruine per day was around 6.28-5.8γ, proving to be 1.3 times that of the control. In this instance, the quantity per 1,000 calories of non-fatty substance taken in by B(1) remaining in the body amounted to about 0.68-0.64 mg, proving greater than that in the control (0.45-0.47 mg). 2. When B(1) was administered in various under the hot environment, the pyramin content excreted in the urine increased in proportion to the increasing dose of B(1), but the degree of the increase, being only slight, differed not much from that of the control. The amount of B(1) excreted in the urine, when the B1 dose was increased to 40γ or 80γ, was 6.4γ and 26.1γ respectively, each value proving to be 1.3 times that of the control (4.4γ and 21.3γ respectively). 3. When the common foods was given freely under the hot environment, the B1-content and pyramin-content excreted in the urine were 4.9-5.8γ and 3.8-3.9γ respectively, both being less than the respective values in the control (6.2-7.2γ and 4.7-4.2γ). This seems to be due to the decrease in the food intake with the attendant decrease in the amount of B(1)-intake. 4. The gain in the body weight and the amount of food intake in the case of the albino rats under the hot and highly humid environment were for poorer than those of the control raised under the normal environment.