THE ASSOCIATION of established chronic lymphatic leukemia or lymphosarcoma with hypogammaglobulinemia (HGG) is well known.1-3 The late development of a lymphosarcoma or leukemia in patients with clinically preexisting congenital or acquired hypogammaglobulinemia is a much rarer event. The purpose of this paper is to present the case of an adult patient with idiopathic acquired HGG of five years' duration, who was extensively studied during the period of HGG and who ultimately developed lymphosarcoma. The occurrence of lymphosarcoma in patients with clinically preexisting HGG raises the question of the existence of common factors, which may link these two unusual diseases. Another interesting feature of this patient's disorder, that has not been previously reported, was that the tissues of this patient contained large amounts of γ-globulin. Report of Case The patient was a 50-year-old white woman who was admitted to Montefiore Hospital for the first time in January 1957 because of