Fat emulsion has been widely accepted a parenteral nutrient for the prevention of essential fatty acid deficiency and the supply of a high energy source. The following problems associated with the administration of fat emulsion are, however, well recognized: 1) The soy protein detected slightly in soy bean oil may induce allergic reactions. 2) Although administered in small quantities emulsified fat particles over 5 microns in diameter can cause fat emboli, including as pulmonary, splenic, placental, and cerebral emboli. 3) Hyperlipidemia may cause pulmonary hypertension and hemophagocytosis when triglycerides contained in the fat emulsion are intravenously administered at a rate greater than 0.1g/kg/hour. 4) Fat emulsion may have immunosuppressive effects, because emulsified fat particles phagocytized by the reticuloendothelial system reduce its functions. Long-chain triglyceride of the omega-6 series can suppress the functions of lymphocytes and neutrophils through prostaglandins. 5) Fungal infections, especially with Malassezia furfur which requires fat for growth, are sometimes associated with intravenous fat emulsion infused through a central venous catheter.