The discovery of metabolic functions of creatine in muscle metabolism has attracted considerable clinical interest in the study and treatment of disorders of the muscular system, particularly in pseudohypertrophic muscular dystrophy and myasthenia gravis. This subject was reviewed by Harris and Brand1 in a recent issue of The Journal. Evidence is gradually accumulating, however, which indicates that the metabolism of creatine has a wider clinical importance than in the specific myopathic diseases. Changes in creatine excretion have been noted in individuals not suffering from disorders of the muscular system. A detailed discussion of these changes and their significance in the various phases of normal and pathologic physiology may be found in the writings of Hunter2 and Rose.3 It seems likely that creatinuria in the human being is related to defective creatine storage in muscle or to abnormally high creatine synthesis. Creatinuria occurs in all types of muscular