Lipfanogens (so designated by the authors) are present in blood serum, and are believed to be involved in the deposition of fat in atherosclerosis. An important factor in the reduction or prevention of fat deposition is the antilipfanogen also present in blood serum. This agent opposes the action of the lipfanogens in the formation of fat granules. Dr. Simms, Dr. Parshley, and Mrs. Pitt have devised methods for quantitative determination of lipfanogens and antilipfanogen by use of specially prepared tissue cultures of adult fibroblasts free from fat granules. This paper describes current methods of preparation, purification, and properties of lipfanogens and antilipfanogen.