Diarrhea is a major cause of mortality and morbidity affecting infants and children in many parts of the world. Research and understanding of normal and abnormal gastrointestinal physiology allowed the development of oral electrolyte solutions to treat dehydration. These solutions were initially used for treatment of cholera in areas with poor access to medical care and are now used extensively by the WHO. Therapy with OES has expanded to other nonsecretory causes of diarrhea. Two types of solutions are available in the United States. Maintenance solutions contain 40 to 60 mEq per liter of sodium and are used for prevention of dehydration or after rehydration. Rehydration solutions contain 60 to 90 mEq per liter of sodium and are effective for the oral repletion of fluid and electrolyte deficits in both secretory and nonsecretory diarrhea.