The author analyzes the four main areas of nutritional status assessment in hospitalized patients: 1. Assessment of bodily reserves of energy and protein, 2. Assessment of the functional capacity where damage caused by malnutrition can be assumed, 3. Estimation of the extent of metabolic stress, 4. An attempt to unify the procedure as regards interpretation and prognosis. Clinical research provides many methods and data which can be used for the evaluation and monitoring of the nutritional status, for giving nutritional support by parenteral nutrition of optimal quantity and quality. It is, however, necessary to elaborate feasible diagnostic methods which can be used in special departments as well as in standard hospital practice.