Lysolecithin comprises 9.6 and 21.5% of thephospholipids of the plasma of man and rat, respectively.Ultracentrifugal and gel filtration studies showed that themajor portion of the lysolecithin is not found together with theother phospholipids in the plasma lipoproteins. By zone electrophoresis, gel filtration, and ammonium sulfate fractionation, it was found that lysolecithin was consistently associatedwith albumin fractions. Immunoelectrophoretically homogeneous rat albumin was prepared. It contained 0.5 mg of lipidphosphorus per g of protein; 98.3% of this lipid was lysolecithin. It is concluded that lysolecithin is transported in plasmabound to albumin.