THE DEMONSTRATION of the importance of the content of solutes in the food of infants has introduced a new and important consideration in infant feeding. It is now apparent that a formula or diet satisfactory in all other respects may, under certain circumstances, be detrimental to the infant because of the excessive load of solutes presented to the kidney. Such circumstances include principally the feeding of unusually large amounts of electrolytes and protein to normal infants exposed to relatively high environmental temperatures for prolonged periods of time or to infants with renal insufficiency. The purpose of the present communication is to consider whether any practical advantage is achieved by feeding a normal infant, in a normal environment, a formula containing fewer solutes or relatively more water than are contained in one composed of cow's milk and carbohydrate in the usual proportions, fed at a concentration of 150 ml/100 cal (20 cal/oz). From this point of view the question can be raised as to whether there is any advantage in feeding unusually dilute formulas to newborn infants. Origin of the Renal Solute Load The load of solutes requiring excretion by the kidneys is derived almost entirely from the protein and electrolyte in the diet. In Table I the content of nitrogen and electrolytes is listed for human and cow's milk. Also given in the table are calculated values for the approximate quantity of solutes requiring excretion by the kidney. It will be noted that an infant receiving 133 cal/kg from human milk would be required to excrete 14.0 m0sm/kg/day while an infant receiving 133 cal/kg from whole cow's milk without added carbohydrate would be required to excrete 60.9 m0sm/ kg/day. Furthermore, it is apparent that an infant receiving two-thirds of the calories from cow's milk and one-third from added carbohydrate would need to excrete only two-thirds the quantity of solutes excreted by the infant fed cow's milk without added carbohydrate (2/3 X 60.9 = 42.7 m0sm/kg/day).