INTRODUCTION The bibliography of renal glycosuria is already given by one of us.1 In renal glycosuria glucose is excreted in the urine, owing to the descending of the renal threshold, while the carbohydrate metabolism is normal. The renal threshold for glucose is the smallest limit of the content of glucose in the blood, in which sugar is first to be excreted in urine. In diagnosing renal glycosuria, it is essential to determine the content of sugar in the blood and the renal threshold for glucose. We first measured the sugar in the blood of the normal Japanese and then the alimental hyperglycemia in the blood which occurred after giving 100 gm. glucose. In this experiment we discriminated between those who eliminated sugar in the urine after the intake and those who did not. Then, giving again a smaller quantity of glucose to those who excreted sugar, we tried to investigate