We present a research work on the diagnosis of the malabsorption syndrome in childhood. The study is based on two diagnostic tests which are: the xylose test and the histological examination of intestinal mucosa. We have tried to assess the usefulness of the determination of the blood xylose after an extra oral load of xylose, comparing the results with the morphological findings in the intestinal mucosa, making a correlation between both, in order to discern the contribution of this examination to the diagnosis of the malabsorption syndrome in childhood. We come to the following conclusions: The determination of the blood xylose after an extra oral load with a single dose is a useful test in the diagnosis of malabsorption syndromes in childhood, and gives us facts about the status of the intestinal mucosa. The abnormality of the results of this test is an important indication for an intestinal biopsy. The xylose test cannot replace the intestinal biopsy.