Hypersensitivity to physical,1-3 chemical,4-6 and bacteriological7,8 substances, altered cellular metabolism,9-11 and endocrine abnormalities12,13 have been implicated in attempts to explain the pathogenesis of the various collagen diseases. The abnormal metabolism of phenylalanine and tyrosine has now been postulated by Nishimura et al.14,15 as a biochemical clue to the etiology of collagen diseases. The concept of collagen diseases by Klemperer et al.,16-18 which originally included acute disseminated lupus erythematosus, scleroderma, and later, dermatomyositis, has now been extended by Nishimura et al. to include Weber-Christian disease, chronic discoid lupus erythematosus, periarteritis nodosa, acrosclerosis, and rheumatoid arthritis. We were impressed with this proposition and have attempted a confirmation of their work. In 59 cases of the above diseases studied by Nishimura et al., they detected a substance in the urine which they identified provisionally as 2,5-dihydroxyphenylpyruvic acid (hereafter designated 2,5-DHPPA). This substance was not found