<h2>Summary</h2> The case of a patient with severe burn is reported. Two episodes of symptoms of dehydration developed in which loss of sodium chloride without loss of water was produced by placing the boy in a continuous tub containing hypotonic salt solution. Symptoms of dehydration were due to loss of extracellular electrolyte without loss of body water. Metabolic studies are reported on a patient with infantile diarrhea, which show that the symptoms of intestinal intoxication were brought about by loss of sodium and chloride without deficit of body water. Therapeutic procedures for the treatment of dehydration are discussed in the light of recent concepts of the nature of dehydration.