Alkali-treated lipopolysaccharide from Brucella abortus S1119.3 coupled to agarose beads by cyanogen bromide activation resulted in an immunoadsorbent with which a large amount of B. abortus-specific antibodies could be purified. The method described gave alkali-treated lipopolysaccharide binding efficiencies of up to 98%. There was little loss of alkali-treated lipopolysaccharide from the column after several pH shifts, allowing the immunoadsorbent to be regenerated and used repeatedly.