Immune modulating properties of parenteral lipid emulsions seem to contribute to the increased risk for infections which remains associated with the use of total parenteral nutrition. Emulsions based on soy bean oil (SO) are the oldest and still most widely used lipid source in TPN formulations but their high content of omega-6 polyunsaturated fatty acids (PUFAs) may be a drawback. Fish oil-based lipid emulsions (FO), rich in omega-3 PUFAs, has been approved for parenteral nutrition in many countries. Mainly retrospective studies on clinical outcomes in septic and postoperative patients have suggested clinical benefits with the inclusion of FO in parenteral nutrition regimens. The exact mechanisms behind the beneficial immunological effects of parenteral FO have, however, not yet been elucidated.