1. The heterophile agglutinin could be characterised by a specific antiserum.

2. On account of its broad agglutination spectrum and haemagglutination inhibition studies a heterophile multispecificity of the combining site is postulated.

3. Immunologic parameters used were: concentration of IgA, IgG, IgM, isoagglutinins, heterophile antibodies, agglutinins against staphylococci, E. coli and pertussis, serum opsonins for E. coli and pneumococci, serum hemolytic complement activity, B- and T-subpopulations of lymphocytes, inhibition of migration of mononuclear cells with E. coli.