Fourty-five dogs were subjected to massive hemorrhagic stress by the bottle reservoir technique applied on the femoral artery, and when hypotension of 50mmHg was maintained the course may be divided into the bleeding and backflow stages. In those stages and after blood transfusion 100cc per Kg of 5% glucose solution or normal saline solution were administered, and the influence of the fluid administration upon the plasma and urine electrolyte balance was observed by sampling the blood and urine successively for 4 hours after the fluid administration.1) During hemorrhage the palsma Na decreases slightly the plasma Cl increases somewhat in both stages of bleeding and backflow, while the plasma K shows a prominent increase, especially in the backflow stage. Cases with excessive decline of Na to K ratio die rapidly.2) The influence of readministration of the preserved blood in the bleeding stage upon the plasma and urine electrolyte balance is definitely small and there is a remarkable tendency for recovery, contrary to that in the backflow stage.3) The fluctuation of the electrolyte balance is small in degree in the control cases of blood transfusion without fluid, administration while it is clear that massive administration of fluid influences the electrolyte even in the early stage of hemorrhage.4) Fluid administration with return of blood in the bleeding stage flow consists of normal saline solution and 5% glucose solution, and there is a copious amount of urination while there is not a remarkable change in the level of the plasma K. The glucose solution does not contain Na or Cl, while the normal saline solution contains both of them. After fluid administration, therefore, the plasma Na and Cl decline slightly in the former and augment somewhat in the latter, though they recover the original level promptly without making a remarkable change. As for electrolyte excretion in the urine, administration of normal saline solution induces excretion of Na and Cl while that of glucose solution scarcely influences it.5) In cases with blood and fluid administration in the backflow stage, oliguria or anuria persists and there is a remarkable influence upon electrolyte balance and circulation. Administration of 5% glucose solution, in particular, is prominently associated with exhaustion of electrolyte balance and failure of the renal function.