A new type of polyagglutination is described in which the T and Tk receptors are both exposed on the erythrocyte membrane. It is suggested that there may be an association between this type of polyagglutination and infection by Bacteroides fragilis.

Tk polyagglutinable erythrocytes are described in which A and H activities were reduced. It is suggested that Bacteroides fragilis isolated from cultures of the patient’s blood was responsible for each of these membrane modifications.