Providing very low birthweight neonates with adequate nutrition carries a sense of urgency in view of the substantial nutritional needs for the rapid tissue growth which characterizes this period of development. Since available milk-based formulas are unable to satisfy these neonates' needs, total parenteral nutrition has been relied on heavily to provide adequate nutrition. The recent introduction of fat emulsions for intravenous use has given the neonatologist a tool to provide sufficient calories parenterally while limiting glucose and amino acids to amounts that are well tolerated. Little is known, however, about the very low birthweight neonate's tolerance of fat emulsions. While various regimens are used for the administration of fat emulsions, they are based on habit rather than on scientific data. Although fat emulsions have been used for many years, the available literature sheds no light on the optimal means of administration, i.e., that which produces least changes in the patterns of lipids in plasma. Some clinicians administer fat emulsions continuously over 24 hours in progressively increasing dosages while others prefer to infuse lipids over shorter periods and give the organism a "rest" of several hours; yet a third group do not feel the need to increase the dosage progressively. We propose to assign very low birthweight neonates (750-1000 grams) randomly to one of three widely used regimens of administration of fat emulsions. Patterns of lipids in plasma (total lipids, free fatty acids, triglycerides, free glycerol, cholesterol and infused lipids) will be measured according to a prospective protocol, as will arterial blood gases and bilirubin levels. From these data, we should be able to determine if harmful effects of infusions of fat emulsions on levels of free bilirubin in plasma and on diffusion of oxygen in the lungs occur and at what level of lipids in plasma. We aim to determine (1) which of the three regimens produces least changes in pattern of lipids in plasma, (2) whether changes in plasma concentrations of free bilirubin and oxygen diffusion in the lungs occur in relation to the infusion of fat emulsions, (3) if such changes occur, what constitutes dangerous levels of lipids in plasma, and (4) whether a simple method of identifying which neonates receiving fat emulsions are in dange can be devised.