A coagglutinating reagent has recently been developed and utilized in capsule typing of pneumococci. The reagent consists of stabilized staphylococci coated with specific antibody via the gamma globulin Fc-protein A reaction thereby orienting the antibody molecules with the antigen-reactive Fab parts outwards. Reagent staphylococci coated with antibodies directed against streptococcal group-specific antigens have been used in the present investigations. Overnight cultures of streptococci were treated with trypsin and then directly tested for coagglutination of selected reagent staphylococci on glass slides. In all, 179 strains of streptococci were analyzed by the method described. The results were compared with grouping by using Lancefield extracts in counter-immunoelectrophoresis and were shown to agree completely. The coagglutination method described proved to be accurate, rapid, and simple.