Intravenous lipid emulsions as part of Total Parenteral Nutrition, are now standard in most centers. The most frequently used lipid formula contains predominantly long-chain triglycerides (LCT) of n-6 series . Controversy and concern exist about the immunosuppressive effects of this fuel source mainly based on experimental data because clinical studies are sparse. Some investigators have pointed out that this lipid emulsion impair monocyte, lymphocyte and neutrophil functions although these changes seem to be related to quantity and rate of lipid administration. A new lipid emulsion that contains 50% as medium chain triglycerides is available. The impact of this formula on immune function is unknown although some papers suggest that it produces less deleterious effects on immune response than the traditional lipid source. Prostaglandins and leukotrienes have numerous effects on immune functions and mediate many of the hemodynamic aspects of the metabolic response to injury. The use of n-3 fatty acids that produce less immunosuppressive eicosanoids have been studied in experimental model with hopeful results. Despite these conflicting data, almost all authors agree that there are no justification for withholding intravenous lipid therapy because they are safe and effective providing essential fatty acids with a high caloric content. Future studies are needed to define the precise composition of lipid emulsions that may vary in the different pathologic situations.