The Ibc protein fraction of group B streptococci was isolated from the type Ib strain H36B, the type Ic strain A909, and the type Ic strain 335, and examined against antisera by immunodiffusion and immunoelectrophoresis. The fraction from the Ib strain and one of the Ic strains (A909) contained two antigens or groups of antigens, called the α and β antigens, respectively. Strain 335 produced the a but not the β antigen. This was also the case with three other groupBisolates previously classified as type Ic. One type II and one type III strain produced both antigens. The results suggest that group B streptococci producing the Ibc fraction can be subdivided further on the basis of the antigens that are present in that fracti