Immunological and epidemiological characteristics of' MlT and M1T8 (T8, 25, Imp. 19) group A streptococci isolated in Egypt have been described. Both strains possess a common Ml antigen. The M1T8 strains possess a second antigen which has the immunological and biological characteristics of M protein. The MITI strains do not possess this second M antigen. Absorbed rabbit antisera which are specif'ic for this second antigen do not react with extracts of any of the known M protein serotypes. This second antigen is therefore a newly recognized M protein. The MITI and M1T8 strains had mutually exclusive geographical and temporal distributions. This f'inding may have been a consequence of the immunity which occurred after the initial occurrence of the M1T8 strain.