[The difficulties to diagnose a clinical important defect of disaccharidases (author's transl)]

Duodenal mucosa of 100 infants and children was histologically investigated and the activities of dissaccharidases in the mucosa homogenate were determined. In addition, a combined xylose-lactose loading test was carried out and the behaviour of the stools under the test conditions was observed. The results were compared with regard to the clinical importance of an enzyme defect. The rise of xylose in blood gives no evidence for a defect of disaccharidases in the mucosa. The determination of the glucose maximum after a loading test with disaccharides seems rather to lead to false-normal results. The possiblity of a false-pathological interpretation by an exclusive determination of enzymes must be prevented by further gastroenterological examinations.