An eleventh case of heavy (Hgamma1) chain disease (Yok), surviving for more than 10 years and still living showed clinical and pathological findings similar to cases described in the past. The patient was given only glucocorticosteroids, ACTH, antibiotics and gamma globulin, as specific drugs. Precipitation arcs besides the major ones formed by albumin and Fc fragment were disclosed by immunoelectrophoresis. The existence of these minor components were confirmed with antigen-antibody crossed

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... ctrophoresis and Sephadex G-200 gel filtration. They did not form precipitation arcs with the other antigens available and they appeared in the same fractions of IgG on gel filtration suggesting their having higher molecular weight than the major ones. In addition to these findings, the clinical course of the patient is described.