Dietary factors have been shown to contribute to the occurrence or persistence of chronic non-specific diarrhoea (CNSD). Among these are low dietary fat, high fluid consumption, and the consumption of apple juice. Prompted by the clinical impression that freshly pressed and unprocessed ('cloudy') apple juice was less likely to induce diarrhoea than normal, enzymatically processed ('clear') apple juice, both juices were compared in terms of carbohydrate malabsorption, gastric emptying, and effects on defecation patterns. Clear and cloudy apple juice differ in their fibre and non-absorbable monosaccharide and oligosaccharide contents. Ten healthy children aged 3.6 to 5.9 years ingested 10 ml/kg of clear and cloudy apple juice; in five of them it was enriched with 40 mg of [1-13C]-glycine. Clear apple juice resulted in increased (> or = 20 ppm) breath hydrogen excretion in 8/10, compared with 5/10 after cloudy apple juice; peak breath hydrogen was higher in the clear apple juice group (35 (4) and 18 (3) ppm, respectively). Gastric emptying as determined by means of labelled breath carbon dioxide (13CO2) excretion was similar with both juices. In a four week crossover clinical trial 12 children, formerly diagnosed as having CNSD, were given extra clear fluids (excluding fruit juices; > or = 50% over basal consumption), clear apple juice, or cloudy apple juice, for five day periods. Extra fluids and cloudy apple juice did not influence stool frequency and consistency compared with the basal period. In contrast, clear apple juice significantly promoted diarrhoea. It is suggested that, in addition to fructose, the increased availability of non-absorbable monosaccharides and oligosaccharides as a result of the enzymatic processing of apple pulp is an important aetiological factor in apple juice induced CNSD.