Na, Cl, and NaCl deficiencies were produced in pigs with a resultant decrease in daily gains and in efficiency of feed utilization. The NaCl deficiency was no more severe than the Na deficiency alone. Blood plasma studies of the Na concn. indicate that blood plasma Na cannot be used positively to detect a Na deficiency. The Cl deficiency caused a significant decrease of the blood plasma chlorides. Coincident with the severe Na deficiency was a significant rise of K in the blood plasma. The growth data for the Na and the balance studies for Na, Cl, and K suggest that the requirements for growing swine making avg. daily gains of approx. 1.35 lbs. are 36-42 mg. of Na, 53-64 mg. of Cl, and 100-120 mg. of K per kg. body wt. daily.