Important condition for a parenteral, enteral or parenteral-enteral nutrition, especially in patients before extended operations of during conservative therapy, is an exact nutritional assessment before beginning of this therapy. By means of biochemical examinations (visceral proteins), anthropometric measurements (body mass, triceps skinfold, arm muscle circumference, creatinine index) and immunological methods (total lymphocyte count in the blood, skin testing with test antigens) it is possible to classify nutritional conditions in severity and kind of malnutrition. By evaluating the digestive and resorptive capacity it is possible to determine the way of application.