In this study an albumin-containing lipoprotein is isolated by column affinity chromatography and electrophoresis. Its electrophoretic mobility is faster than that of albumin in agarose gel. Immunologically it reacts with anti-albumin and anti-apolipoprotein-A-I. No reaction is obtained against antibodies to any of the other previously known lipoportein families: Apo-AII, Apo-B, Lp(a), Apo-C, LpX, Apo-D or Apo-E ('the arginine rich peptide'). It differs from purified albumin in having higher amounts of glycine, serine and glutamic acid. Moreover, the molecular weight is estimated to 80,000 as compared to 67,000 for albumin.