Dumping syndrome is rarely seen in children. We studied ten children with symptoms following various types of gastric surgery. All had abnormal blood glucose and breath hydrogen responses after oral glucose challenge, indicating reduction of both glucose tolerance and glucose absorption, as compared to controls. Glucose tolerance was best expressed as the difference between peak and subsequent lowest blood glucose level, the upper limit of normal (mean + 3 SD) being 5.9 mmol/l. In eight children with persisting symptoms we tested the effects of glucomannan, a highly hygroscopic tasteless fibre, on glucose tolerance and glucose absorption. Glucomannan significantly improved glucose tolerance, but did have no overall effect on glucose absorption. Four children tested glucomannan added to the main meals. Breath hydrogen excretion, as established with the daytime breath hydrogen profile, decreased significantly in two, but complaints increased in three children. Glucomannan does not appear to be suitable for the treatment of dumping syndrome in children as the side effects seem to overrule the beneficial effects.