Twenty patients fasted for different periods as part of treatment for their obesity; they took water, or coffee or tea with artificial sweetener. Three who took 180 m-equiv. NaCl on one day during fasting excreted more Na and in one the extra Na excreted on the day after the salt was taken exceeded the dose. When 600 kcal mixed diet or glucose was taken excretion of Na promptly fell. Loss of weight ceased when salt was taken, and 2 patients gained 1.5 to 2 lb despite absence of food.