Strains representing each of the five serologically distinct types of group B Streptococcus and variant strain 090R, which is devoid of type-specific polysaccharide, were studied by electron microscopy after incubation with various ferritin-conjugated antibodies. Ferritin-conjugated types Ia, II and III antibodies localized on homologous cells in a pattern that defines the capsular location of the type Ia, II, and III polysaccharide antigen. Type Ib and Ic cells have surface antigens to which ferritin-labeled antibodies to both capsular polysaccharide and a common surface protein attach.