One hundred four healthy premature infants, of birth weight 1,000 to 1,800 gm, were fed one of five feedings: (1) human milk; (2) human milk plus 13 meq/l of sodium chloride; (3) human milk plus 13 meq/l of sodium chloride and 18 meq/l of potassium chloride; (4) a half-skimmed cows milk formula; and (5) a partially-skimmed vegetable oil, cows milk formula. The infants fed any of the three human milk formulas gained weight at a slower rate than the infants fed either of the two cows milk formulas. Infants whose diets were changed from unmodified human milk to the half-skimmed cows milk gained large amounts of weight, and at times were visibly edematous. Infants whose diets were changed from the human milks with added sodium chloride, to the half-skimmed cows milk, gained lesser amounts of weight and did not become edematous. The infants fed the two cows milk diets gained similar amounts of weight, although one diet provided 6.5 gm/kg/day, the other 3.1 gm/kg/day of protein.