1. Thirteen strains of hemolytic streptococci isolated from patients with acute rheumatic fever did not show any evidence of being related serologically.
2. Strains of hemolytic streptococci exist which, although identical by the agglutination test, do not show complete reciprocal agglutinin absorption. Sera prepared from such related strains may show some protective power in mice against another member of the group.
3. Some strains of hemolytic streptococci may absorb agglutinins from a serum prepared against another strain, and yet may fail to be agglutinated by that serum.
4. None of 20 strains of hemolytic streptococci isolated in New York City in 1924, and 1925, corresponded serologically with Dochez, Avery, and Lancefield's 4 type strains or with Gordon's Type I strain.