Dehydration resulting from diarrhea remains an important cause of morbidity and mortality among infants and children worldwide. Although it is well established that rapid and generous intravenous restoration of extracellular fluid, followed by oral rehydration therapy (ORT) should be used in children with severe dehydration, physicians continue to be reluctant to use such therapy. Applying the principle of body fluid physiology to the current treatment of dehydration, we developed a simple and yet effective treatment strategy to fluid therapy for children with diarrheal dehydration using commercially manufactured solutions. Children with mild-to-moderate dehydration are best treated with ORT using commercially available oral solutions containing 45-75 mEq/l of Na(+). Children who have clinical evidence of severe dehydration should receive intravenous fluids, 60-100 ml/kg of 0.9% saline in the first 2-4 h to restore circulation. Oliguric patients with severe acidosis should receive a physiological dose of bicarbonate to correct blood pH level to 7.25. Once circulation is restored, the ORT should be given in small quantities to replace losses of water and Na(+) over 6-8 h. Age-appropriate diet should be started as soon as tolerated. Those who cannot tolerate ORT should receive intravenous rehydration for the remainder of the deficit and maintenance. Addition of 20 mEq/l K(+) to rehydration solutions permits repair of cellular K(+ )deficits without risk of hyperkalemia. The amount of Na(+) given to replace maintenance and deficit fluids varies with the forms of dehydration. Isonatremic dehydration is best treated with 5% dextrose in 0.45% saline containing 20 mEq/l KCl over 24 h. Hyponatremic dehydration is best treated with 0.9% saline and 0.45% saline alternately in a 1:1 ratio in 5% dextrose containing 20 mEq/l KCl over 24 h. Hypernatremic dehydration is best treated with 5% dextrose in 0.2% saline containing 20 mEq/l KCl over 2-3 days to avoid cerebral edema. Maintenance hydration is best treated with 5% dextrose in 0.2% saline containing 20 mEq/l KCl. Ideal commercial intravenous maintenance and deficit solutions have yet to appear.