Abstract
Purified [gamma]G globulin fraction of normal, and of infectious mononucleosis serum contained heteroantibodies combining with sheep, horse, rabbit and ox erythrocytes. Despite considerable differences in agglutinin titers the amount of antibody in the [gamma]G globulin fraction combining with these cells was of the same class of magnitude. The majority of the [gamma]G heteroantibodies in infectious mononucleosis serum had the same serological specificity as the [gamma]G heteroantibodies of normal serum.