An episode of diarrhea causes weight loss and a temporary cessation of growth in infants and children. Diarrhea is accompained by malabsorption of sugars, nitrogen, fats, and micronutrients. The mechanisms by which acute diarrheal disease produce malabsorption have not been studied carefully. The nutritional costs of malabsorption may pose a major threat if diarrhea becomes chronic or recurrent. The hydrogen breath test for carbohydrate malabsorption does not require intubation or blood drawing and can be used in children to help clarify the importance of carbohydrate intolerance in the duration and perpetuation of acute diarrhea and intestinal bacterial overgrowth.