Ninety-four well-nourished, bottle-fed infants with hypernatremic (N = 61) or hyponatremic (N = 33) diarrheal dehydration were treated with oral rehydration. In 61 hypernatremic and 25 hyponatremic infants, two thirds of the fluid volume were given as glucose/electrolyte solution containing 90 mmole of sodium per liter and one third as plain water; the other eight hyponatremic infants were given glucose/electrolyte solution alone. Fluid deficits were successfully and rapidly replaced with oral therapy alone in all 61 hypernatremic infants (mean +/- SEM, 8.5 +/- 0.6 hours) and in 31 of those with hyponatremia (mean +/- SEM, 10 +/- 1.2 hours). Two hypernatremic infants required some intravenous (IV) fluids. The mean serum sodium levels fell in the hypernatremic infants to normal and rose in those with hyponatremia. Only five (8%) of the 61 hypernatremic infants manifested convulsions during oral rehydration; this compared favorably with the 14% rate of convulsions encountered previously when we used IV rehydration.