This prospective study comprises 40 infants with severe hypernatremic dehydration due to gastroenteritis. During the first 24h, natremia was closely monitored and infusion rates were adjusted so as to keep the rate of fall in natremia below 0.5 mEq/l/h. This could be achieved by giving a 70 mEq/l Na solution at the rate of 120 ml/kg/24 h. Rehydration was uneventful in all cases, and no convulsions were observed.