IgE (PS) myeloma protein was digested with papain for various lengths of time. After 1 h, several components of the IgE could already be demonstrated. After 3-11 h of digestion Fc, Fc′ fragments and a third component tentatively termed Fx were obtained. The Fc′ component showed partial identity with the Fc fragment, in the immunoelectrophoresis demonstrated faster mobility than the Fc fragment, had a molecular weight of approximately 58,000 and could not block passive sensitization of human skin by reaginic antibody. Thus far the Fx component was not obtained in a pure form. This component was demonstrated only in immunoelectrophoresis and had a slower mobility than the Fc and Fc′ fragments. For the time being it is not clear whether the Fx is a F(ab′)2 fragment or a part of it, or is a third component of the Fc fragment.