The group B streptococci (GBS) are known to have type-specific polysaccharides rich in N-acetylneuraminic acid end groups, which are thought to be important immunological determinants. Wheat germ agglutinin (WGA) has affinity for N-acetylneuraminic acid as well as N-acetylglucosamine, and readily precipitates the type but not the group polysaccharide. A WGA-Sepharose affinity column was used to isolate complete type polysaccharides of representative strains of the 4 major GBS types. WGA, other lectins, and rabbit antisera were then used to characterize the products of various extraction procedures and chemical degradations, including mild acid hydrolysis and treatment with neuraminidase. Results of lectin binding studies were consistent with proposed chemical structures of types Ia, Ib and II. Differences were noted, however, between the cross-reactive antigens of pneumococcus type 14 and the desialated GBS type III polysaccharide. Although structurally similar, indirect evidence from lectin binding studies suggest that these antigens may not be identical.