Each year, millions of children die of diarrhea. Many more suffer frequent diarrheal illnesses, which stunt their growth and add to the problems of their often overburdened parents. Nonetheless, there have been substantial reductions in deaths from diarrhea, primarily as a result of the development and use of a standard oral rehydration solution (containing 90 mmol of sodium and 111 mmol of glucose per liter; total osmolality, 311 mOsm per kilogram). Actively promoted by agencies including the World Health Organization (WHO) and the United Nations Children's Fund, this inexpensive but efficacious treatment is now accessible to nearly everyone in practically. © 1995, Massachusetts Medical Society. All rights reserved.