A conglutinating system present in normal bovine serum has been shown to consist of antipolysaccharide, conglutinin and complement. Conglutinated dextran yielded conglutinin, C′1 and C′4 on extraction with EDTA, and both high and low molecular weight antidextran on extraction with maltose. Details of the chromatographic purification of conglutinin and the high and low molecular weight antidextran are given. The isolated conglutinin was essentially homogeneous by free electrophoresis and by ultracentrifugation, but was heterogeneous immunochemically. Conglutinin migrated as a γ-globulin, had a sedimentation constant of 6.6 and a molecular weight of 650,000.