Summary Various preparations of normal and antibody guinea pig γ1 and γ2 globulins have been analyzed for their hexose content, using the indol method. The value obtained, when expressed in glucose equivalents, was 0.74% for both types of γ-globulin. Analysis of the different fragments obtained by enzymatic splitting of the molecule of γ2 globulin indicated that most of the hexose was contained in the fast (F) fragment obtained after digestion with papain (piece III of Porter). The fragment obtained after pepsin digestion contained very little if any hexose. The results indicate that guinea pig γ1 globulin does not correspond to the γ1A globulin of man and mouse. It is suggested that γ1 globulin represents a distinct family of im-munoglobulins, possibly also existent in other animal species, which mediates anaphylactic reactions within the species.