1. Lipoprotein B from female Lp(a)-lipoprotein-negative serum was isolated from the fraction of density 1.073–1.125 by using immunoadsorbent; 2.5mg of freeze-dried material was obtained from 100ml of serum from a fasting patient. 2. The hydrated density of this lipoprotein was found to be 1.084g/cm3. A flotation rate F1.200 of 9.4 and lipid/protein ratio 1.40 were found, similar to that of high-density (d 1.073–1.125) lipoprotein preparations. 3. From immunochemical and electrophoretic studies of the intact and totally delipidized lipoprotein B it was concluded that this lipoprotein represents a separate family within the high-density range of human serum lipoproteins. 4. The possibility that the isolated lipoprotein B is an artifact created by the isolation procedure is discussed.
