30 intensive-care surgical patients were randomly divided into two groups. Metabolic substrates, nitrogen balance, energy balance, and gaseous exchange were measured. Both groups were investigated under the following conditions: 1. our routinely administered parenteral diet (1.5 g amino acid . kg-1 . d-1 and 7.6 g carbohydrate kg . d-1) 2. an infusion regimen containing an increased amount of carbohydrates, clearly exceeding energy expenditure (1.5 g amino acids . kg-1 . d-1 and 12 g carbohydrate . kg-1 . d-1) and under a two-fold aminod-acid intake (3.0 g . kg-1 . d-1 and 7.6 g carbohydrates . kg-1 . d-1). The energy expenditure of the patients in the two investigated groups averages 3000 kcal . d-1. We can cover this energy expenditure with an increased carbohydrate intake of 12 g . kg-1 . d-1. However, the data observed from the gas exchange measurements--the RQ remained still about 0.9--and urea-nitrogen excretion, suggest that even an excessive administration of carbohydrate does not totally suppress the participation of endogenous fat and protein in the oxidative energy-production process. By administering 3.0 g amino acids . kg-1 . d-1 nitrogen balance can be achieved, but leads to further elevation of BUN levels; while nitrogen excretion is not markedly increased when compared to the patients receiving 1.5 g amino acids . kg-1 . d-1. These results seem to indicate that nearly all of the high amounts of caloric substrates and amino acids are used to meet energy expenditure and nitrogen loss of intensive-care patients in the early period after trauma or severe illness, but they also serve as an additional burden for the extremely stressed metabolism in this situation.