Urinary excretion of total amino acids was measrued in normal and diabetic rats, streptozotocin-induced diabetic rats excreted increased amount of urinary total amino acids and nitrogen. This suggested increased degradation of body protein. Although excretion of total amino acids increased in the diabetic rats, the amino acid pattern of amino acids for both groups were very similar. The efficiency of dietary protein utilization was significantly lower in diabetic rats then that of normal rats. Streptozotocin injeciton affected the urinary excretion of 3-methylhistidine whereas diet did not. These findings suggest that the rate of urinary excretion of total amino acids can be empolyed as an index of protein metabolism, particulary as a simple index in the assesing the status of protein nutrition.