Despite the widespread interest in malnutrition in the elderly, the utility of laboratory tests is limited. This is because their diagnostic significance can be impaired by undercurrent diseases, pre-analytical effects and unsatisfactory standardization. This survey summarizes the most important parameters of malnutrition. Thus, "nitrogen balance" is considered the golden standard of nutrition status, while the diagnostic significance of serum proteins depends on their biological half-time. Albumin is seen as the most reliable malnutrition marker, but cholinesterase and cholesterol-decrease must also be mentioned. The so-called "low-T3-phenomenon" which is caused by the production of "reverse T3", seems to be the unique parameter for the "catabolic" state of metabolism. Of special interest are also prognostic markers of mortality, such as orosomucoid. Cytokines, other signal peptides, trace elements and vitamins are from the diagnostic point of view of rather limited significance. In sum, the diagnosis and monitoring of malnutrition in the elderly represents an important challenge for laboratory medicine.