The surgical procedures have a great influence on organism and especially its water and electrolyte metabolism. It is considered to be due to glucocorticoids (cortisol) through adrenocorticotrophic hormone (ACTH), mineralocorticoid (aldosterone) through volume-receptor and antidiuretic hormone (ADH) through dicencephalon and posterior pituitary lobe. The purpose of this paper is to investigate the effects of these hormones on water and electrolyte metabolism in normal human subjects.All experiments were performed in normal subjects under water diuresis which was produced by water intake and drip infusion of 5% dextrose solution. Urine flow, osmolality and electrolytes, i.e. sodium, potassium, chlorine, calcium and magnesium, of urine and blood plasma, and, moreovere, creatinine clearance were measured.The intravenous injection of cortisol induced an increase in urine flow, which would be due to an increase in free water clearance (CH2O), not due to osmolar clearance (Cosm). The excretion of urinary sodium and chlorine tended to decrease and potassium to increase. The calcium and magnesium excretions were increased. The excretion of urinary sodium, however, seems to depend on the amount of cortisol. 200 mg of cortisol showed a tendency to decrease in sodium excretion, while 100 mg to increase. Creatinine clearance (GFR) was not changed at all. Plasma level of all electrolytes was also not changed.The urine flow was increased by intravenous injection of aldosterone just like by cortisol. The increase seems to be due to an increase in CH2O, because creatinine clearance (GFR) showed no change and Cosm was decreased. The urinary excretion of sodium and chlorine was decreased and potassium tended to increase. Concerning urinary calcium and magnesium they were increased or not changed. Plasma level of electrolytes showed no change, too.Pitressin® (ADH) promptly induced a marked decrease in urine flow and CH2O. The latter became negative and the ratio of urinary and plasma osmolality (Uosm/Posm) was elevated remarkably. The marked decrease in urine flow seems to be due to the decrease in CH20, because osmolar clearance was not changed. The urinary sodium excretion was decreased or not changed. Chlorine, potassium, calcium and magnesium tended to decrease in urine. Plasma level of electrolytes showed no change. When arginine-vasopressin a synthetic ADH, was administered instead of Pitressin®, the results were just the same as by Pitressin ®. Nicotine is considered to release ADH through its stimulation of hypothalamus. When nicotine was injected intravenously, urine flow, CH2O, Uosm and Uosm/Posm showed the same changes as by injection of Pitressin®. Urinary excretion of electrolytes and plasma level of electrolytes were hardly changed. Creatinine clearance also showed no change.The effects of combined administration of these hormones on water and electrolyte metabolism were investigated. When cortisol and aldosterone were administered together, urine flow and CH2O were increased, while Cosm, was not so changed. Concerning urinary electrolytes, sodium excretion decreased and potassium excretion increased gradually. Urinary excretion of calcium and magnesium showed no constant changes. Creatine clearance was not changed. Thus, the combined administration of these two hormones induced almost the same changes as either of these alone. The administration of Pitressin® combined with cortisol, aldosterone or both showed a marked decrease in urine flow and a marked increase in Uosm/Posm, whereas Cosm, was not changed. Therefore, the effects of Pitressin® seems to appear predominantly.