It is shown that some selected streptococci are agglutinable by soluble antigen‐rabbit antibody complexes owing to the interaction between the streptococci and immunoglobulins, irrespective of the antibody combining sites. Increased agglutination titer of rabbit anti‐egg albumin serum for the streptococci was obtained by addition of egg albumin, but not bovine or human albumin. The agglutination of the streptococci was diminished by addition of preimmune serum or by trypsin treatment of the streptococci; trypsin treatment diminishes the capacity of the streptococci to take up125′I labelled IgG myeloma protein. The effect of variation of the egg albumin concentration and the effect of the ratio between antibody N and egg albumin N was shown. The possible mechanism of the agglutination of the streptococci by immune complexes is sugg