Human plasma low- and high-density lipoproteins were found to bind to Sepharose gels containing coupled cholesterol or cholic acid. The lipoproteins were bound very strongly, and it was not possible to elute them under non-denaturing conditions. The detergents Triton X-100 and sodium dodecyl sulphate eluted the lipoproteins in partly denatured form. Adsorbents were used where the steroid was coupled through a spacer containing a thiol ester bond. It was thus possible to elute bound lipoproteins by selective cleavage of the bond with hydroxylamine. A small proportion of albumin was the only contaminant detected, the amounts depending on which ligand was used. Low- and high-density lipoproteins were separated by gel filtration. They behaved as did the native molecules when analysed by gel filtration, immunodiffusion, immunoelectrophoresis and electrophoresis in polyacrylamide gradient gels. The high capacity and the selectivity of the adsorbents make them suitable for the removal of lipoproteins from protein solutions.