The intravenous administration of fat emulsions has come to be an accepted method for supplying calories to patients who cannot take food by mouth. From the onset, the preparation of intravenous fat emulsions has been a difficult problem. The first difficulty arises in the preparation of a stable emulsion. The high interfacial tension between fat and water makes it necessary to add emulsifying agents. These surface-active agents make possible the preparation of an emulsion of fine particle size. Emulsifying agents are toxic in direct proportion to their ability to lower surface tension.1 Therefore, the best emulsifying agents are the most toxic. Lipid is an integral part of the cell membrane. The emulsifying agents tend to widen the interstices between the lipid molecules in the cell membrane and in this way to increase the permeability of the cell. They may even cause the dispersion of the lipid portion of the