The optimal diagnostic strategy of malabsorption syndrome is not set. The choice should be individualized and the order of execution of different tests available depending on the suspected etiology. The presentation may vary considerably from steatorrhea and severe weight loss to subtle changes in laboratory test results. As specific tests for suspected global malabsorption, d-xylose guides to the existence of a diffuse intestinal disease. The capital diagnostic test in suspected bacterial overgrowth is the hydrogen breath test after glucose administration. In case of suspected intolerance to carbohydrates, the diagnostic test is lactose tolerance test or hydrogen after administration of lactose.