The existence of a cell receptor which recognises plasma high density lipoprotein (HDL) has been suggested from studies which demonstrate specific binding of HDL3 to cultured cells derived from various tissues in the body. This study provides evidence of a specific HDL-binding protein in crude plasma membranes prepared from rat kidney and liver. Following separation of solubilised membrane proteins on polyacrylamide gel slabs and 'Western' blotting, one major band was identified which bound HDL3, or apo AI or apo AII. The protein, which was present in both liver and kidney membranes, was partially purified by repetitive preparative SDS-polyacrylamide gel electrophoresis and although accompanied by considerable loss of binding activity, could still be detected by the ligand-blotting procedure used initially to detect its presence in cell membranes.