Although oral glucose-electrolyte solutions containing 90 mmol of sodium per liter have been widely used in the treatment of acute diarrhea among under-nourished children in the developing world, they have rarely been studied in well-nourished children. We therefore conducted a controlled randomized study among well-nourished children three months to two years who were hospitalized with acute diarrhea (52 in the United States, and 94 in Panama), to compare the efficacy of this solution with that of one containing 50 mmol of sodium per liter and with standard intravenous therapy. Oral rehydration with both solutions according to protocol was successful in 97 of 98 children (one required unscheduled intravenous therapy), and in 87 (89 per cent) no intravenous therapy was required. All of six children admitted with hypernatremia were successfully treated with oral therapy alone. We conclude that glucose-electrolyte oral solutions containing either 50 or 90 mmol of sodium per liter are effective and safe in the treatment of well-nourished children hospitalized with acute diarrhea, and that they may completely replace the intravenous fluids in the majority of such children.