Two patients with severe granulocytopenia and recurrent infections of the skin and oropharynx had excess T lymphocytes with receptors for the Fc portion of IgG (T gamma cells) in blood and bone marrow. The abnormal T gamma cells killed antibody-sensitized target cells in vitro (killer-cell activity) but did not suppress immunoglobulin production by B lymphocytes (suppressor-cell activity). T gamma lymphocytes from normal persons showed both killer-cell activity and suppressor-cell activity. In the serum of one patient, granulocyte antibodies, possibly of an autoimmune nature, were detected. The clinical picture in conjunction with the hematologic and immunologic findings characterized the disease of both patients as a distinct entity among the chronic lymphoproliferative diseases of T-cell origin.