Affinity adsorbents were obtained by the quantitative immobilization of acidic polysaccharides onto Amino Sepharose. For this purpose, a fraction of the carboxy groups of the polysaccharides was converted into activated esters. Polysaccharides with a high uronic acid content (as sodium salts) are insoluble in DMSO; therefore, they were converted into soluble N,N-diisopropyl-N-ethylammonium salts and so, suitable for the immobilization reaction. Using the resulting adsorbent, anti-polysaccharide antibodies directed against plant polysaccharides were isolated from a human immunoglobulin preparation; the specificity of the isolated antibodies suggests an ability to recognize a conformational epitope within the polysaccharide.