The osmolalities of the urine and the plasma as well as the plasma electrolytes were studied in unoperated goldfish, Carassius auratus, sham-operated animals, hypophysectomized animals, and animals from which the corpuscles of Stannius had been removed. Removal of either the pituitary or the corpuscles of Stannius results in loss of blood electrolytes as evidenced by an elevation in urine osmolality and a decline in the plasma electrolytes. Angiotensin II prevents the loss of electrolytes in fish from which the corpuscles of Stannius have been removed but has no effect on the electrolyte balance of the hypophysectomized animals. The possible role of the corpuscles of Stannius is discussed.