1. Group A hemolytic streptococci have been described which do not agglutinate in anti-T serum because they lack T antigen.
2. Other strains occur which contain T antigen yet do not agglutinate in anti-T serum because T agglutination is blocked by the presence of large amounts of M substance in the streptococci.
3. Strains belonging to a number of types have been analyzed to determine their antigenic composition with respect to M and T antigens.