The urinary excretion of amino acids and their derivatives in cases of Wegener's granulomatosis have been examined, and the excretion of urinary amino acids in such cases was different from normal and reticulum cell sarcoma. In Wegener's cases, the amino acids which were always found in readily detectable amounts totaled 33; urinary phenylalanine was 4-5 times higher than in normal subjects. From these experimental results, we believe that the observation of amino acid excretion into urine is an important indicator for the diagnosis of Wegener's granulomatosis. In addition, the results of quantitative examination on the urinary amino acid excretion were compared with normal and reticulum cell sarcoma. Comparison of the analytical data on urinary amino acids of the normal and patient groups indicated significant metabolic abnormalities of some amino acids at the earliest stage of Wegener's granulomatosis.