A large number of experimental and clinical investigations has shown that an adequate, complete intravenous (i.v.) nutrition can be provided by using an amino acid mixture, glucose or fructose, fat emulsions, electrolytes and vitamins. A brief summary of the various investigations of the necessary quantities of energy and nutrients has been given. Based on these studies, recommendations have been made for the supply of nutrients in complete i.v. nutrition, which will cover the requirements of a patient. In many cases it is difficult or even impossible to infuse the required amount of energy in the form of carbohydrate and alcohol. With fat emulsions, however, it is easy to supply the required amount of energy. An i.v. fat emulsion of choice should have the same properties as chylomicrons. Such fat emulsion seems to be metabolized in about the same way as the fat from the ordinary food. By a complete i.v. nutrition including fat emulsions it is possible to maintain a good nutritional status in most patients as well as to produce growth in infants for reasonably long periods of time in cases when oral feeding is impossible or inadequate. Adult patients have been kept in good nutritional condition for periods up to 7 months on complete or total i.v. feeding. By the use of an adequate complete i.v. nutrition the loss of body protein and body weight in the post-operative period can be reduced to a large extent in the adult patient. In neonates and infants it is possible not only to eliminate the loss of body protein and body weight in the post-operative period, but also to promote formation of new body protein and induce growth by i.v. feeding. A complete or total i.v. nutrition to be looked upon as an alternative to oral food intake should include about 40% of the energy supply as fat corresponding to the amount in the normal food. Up to 60–80% of the energy has been supplied as fat. Total i.v. nutrition with 40% of the energy intake in the form of fat has been maintained during the whole gestation period in dog. Six puppies with no anatomical abnormalities were delivered, three of them survived.