The invention relates to a process for isolating a lectin composition, in particular comprising the mannose-binding lectin (MBL), suitable for using recombinantly produced lectins as starting material, as well as methods for enriching a lectin preparation with respect to high molecular weight lectins. The method implies the use of sugar derivative modified solid supports, wherein the concentration of sugar derivatives on the solid support contributes to the isolation of predetermined oligomers of lectins.