The feeding habits of 70 infants under 6 months old hospitalized with acute gastroenteritis were studied to determine whether current efforts to discourage high-solute feeding were having an effect on the incidence of hypernatremic dehydration. Fifteen infants (21%) were fed modified (low-solute) milks and 55 (79%) unmodified (high-solute) milks. Of 47 infants under 3 months old, 15 (32%) had commenced mixed feeding. Plasma sodium level was estimated in 60 infants. Mean values in the modified and unmodified groups were the same, at 137 mEq/liter. Only one infant was hypernatremic (sodium level, 152 m/eq/liter). Osmolalities of 65 samples of milk were measured to provide a measure of milk concentration. Only ten (16%) exceeded by more than 25% that recommended by the manufacturers. Twenty-two (34%) were less than 75% of the recommended concentrations. These improved feeding practices have probably contributed largely to the very low incidence of hypernatremia by preventing dangerously high solute intakes at a time of particular vulnerability.