A simple radioassay of HDL-binding sites on purified rat liver plasma membranes with polyethyleneglycol (PEG) precipitation separation of B/F was developed. ¹²⁵I-labeled apoE-deficient human HDL₃ was prepared as the ligand. 12.5％ of the final PEG concentration could effeciently sediment the ¹²⁵I-labeled HDL₃-membrane complex, and more than 94％ of the total binding was specific (non-specific binding was determined at the presence of 25fold excess HDL₃). A saturable and high affinity HDL-binding site on liver membranes with kd 14.5+0.86μg/ml (16.6×10^-8mol/L) and B_max 15.6+6.8μgg/mg membrane protein was found. The B_max of this HDL-binding appeared to increase as the reactiontemperature rose. The binding activity of this HDL receptor was not inhibited by 0—30 m mol/L EDTA and not activated by 0—5.0 mmol/L Ca²⁺, as well as insensitive to trypsin. Human HDL₃ and rat HDL, but not human VLDL, LDL and albumin, could effectively inhibit the ¹²⁵I-labeled HDL₃ binding to the liver membranes. The ¹²⁵I-labeled HDL₃ binding activity (μg/mg membrane protein) increased with the increasing of the liver membrane purity. These results suggest that there was a saturable and highly specific HDL-receptor on liver plasma membranes, and its biologic properties are different from LDL-and apoE-receptors.