The possibilities of peripheral-venous nutrition as regards its substrate dosage are limited due to the vein tolerance (osmolarity) of the infusion mixtures. It is, therefore, imperative to achieve an optimum composition of the solution for obtaining the most favourable utilization rate for the organism. We have shown that a dosage below 0.6 g amino acids/kg BW per day does not have a positive influence on the nitrogen balance in comparison to a control group not nourished. The situation of a patient in the post-aggression phase results in 30 to 40% of the supplied amino acids being utilized in the energy metabolism and excreted as urea, in spite of a sufficient simultaneous energy supply. Not only does this uneconomical loss alone necessitate a higher amino acid dosage, but also the additionally increased catabolism of endogenous protein reserves in the post-operative phase. It remains to be tested whether the sole substitution of amino acids in a solution without carbohydrates over a short infusion period constitutes a compromise between the intended peripheral-venous tolerance and an effect on the nitrogen balance.