The studies of Van Slyke and his associates1 have established on a firm foundation the relation between the concentration of urea in the blood and that in the urine of normal persons under a variety of conditions. As a result of these and of similar investigations, it is generally recognized that the urea clearance test is perhaps the most reliable method available for the quantitative estimation of renal functional efficiency. Certain factors have been shown to affect the rate of removal of urea from the blood of normal persons. As demonstrated by Addis and Drury,2 MacKay3 and Van Slyke, Alving and Rose,4 severe exercise may diminish urea clearance somewhat, presumably by diverting an unduly large proportion of blood to muscular tissues, with a resulting diminution in the renal circulation. Moderate exercise, however, as shown by Van Slyke, Alvin and Rose 4 and by Bruger and Mosenthal,