Lactose intolerance and malabsorbed carbohydrate present in some fruitjuice may trigger symptoms commonly seen in irritable bowel syndrome. In a two-site study, 28 subjects 9 months to 18 years old (mean 6.9 +/- 5.9 years) with significant intake of apple juice or pear nectar (> 6 oz a day) with the diagnoses of irritable bowel syndrome, functional abdominal pain, or chronic nonspecific diarrhea were recruited. Breath hydrogen tolerance tests utilizing lactose, sucrose, and apple juice in the amount they typically consumed were positive in 32%, 0%, and 50%, respectively. Subjects were asked to refrain from the ingestion ofjuice for 1 month: 13 of the 28 (46%) subjects improved while 15 (54%) showed no change in their symptoms. In fact, none consuming 6 to 12 oz of apple or pear juice daily improved, 27% of those consuming 12 to 16 oz improved, and 91% of those consuming > 16 oz improved (P < 0.02). Subjects were then given comparable amounts of white grape juice for 1 year. The initial symptoms did not recur in any of the subjects who initially responded to the juice-free diet. Of the 15 subjects who did not respond to the juice-free diet, seven became asymptomatic. Overall, 20 subjects (71%) were asymptomatic, and eight (29%) had no change in their symptoms. Some individuals with irritable bowel syndrome have their symptoms based on their malabsorption of carbohydrates present in apple juice and pear nectar and may improve with adequate choices of fruit juice such as changing to white grape juice.