During recent years, an increasingly important place has been accorded the study of the inorganic elements of the blood in nephritis. Numerous reports of the concentration of the various salts of the blood have appeared. Few, if any, of these include any investigation of the total salt metabolism, and conclusions as to retention, or depletion, of one or the other salt in the body are based solely on its concentration in the blood. It was, therefore, thought to be a matter of considerable interest to determine the total metabolism of the salts in nephritis and its relationship to their concentration in the blood. For the past two years, suitable cases in the Hospital for Sick Children have been investigated in this manner. The number of cases studied has been limited by restrictions such as are imposed when accurate measurements of intake and excretion are essential. Thus, all cases in which