The D-xylose and triglyceride absorption tests have been widely used as screening tests to characterize malabsorption and indicate intestinal biopsy. In this paper we report the efficiency of these tests in the differential diagnosis of the various causes of chronic diarrhea and their possible relationship to jejunal villous atrophy. Two hundred and fifteen children with chronic diarrhea were submitted to the D-xylose and triglyceride absorption tests, and small intestinal biopsy. The patients were divided into 5 groups, that is: I--celiac disease, 53; II--protracted diarrhea, 24; III--environmental enteropathy, 50: IV--celiac disease under gluten free diet, 11; V--irritable bowel syndrome, 77. D-xylose and triglyceride absorption tests were within normal limits in 3.8% and 4.2% patients belonging respectively to groups I and II. On the other hand, only 7.8% of the patients belonging to group V would be included in the group of patients that would have indication for intestinal biopsy, since both tests revealed abnormal results. Moreover, both tests showed an excellent relationship with the intensity of villous atrophy.