Apple juice contains fructose and sorbitol, substances that have been shown to be incompletely absorbed by most people. As this might have clinical consequences, especially in young children, we investigated the absorption of the carbohydrate content of apple juice in apple juice consuming toddlers with chronic nonspecific diarrhoea as compared to controls, using the breath hydrogen (H2) test. Incomplete absorption of the carbohydrates from 250 ml of apple juice, as indicated by a maximum breath H2 increase of greater than or equal to 20 parts per million (ppm), was found in all nine patients (mean +/- SEM 57 +/- 8 ppm), and in five out of eight controls (22 +/- 7 ppm) (P less than 0.01). Six patients were retested with apple juice "enriched" with glucose, which is known to improve fructose absorption. The maximum breath H2 increase as well as the area under the breath H2 curve decreased significantly. It was thus estimated that fructose accounted for 80% of the incomplete absorption and sorbitol for 20%. Elimination of apple juice from the diets of the nine patients resulted in normalisation of both the frequency and the consistency of the stools. Incomplete absorption of the carbohydrates, particularly fructose, from apple juice seems to be quite common, and may contribute to chronic diarrhoea in young children.