A condition with fibrosis of the bone marrow, extramedullary hemopoiesis, and splenic enlargement was described one-half century ago. Its close relationship to chronic granulocytic leukemia and polycythemia rubra vera or its classification as a separate entity has stimulated much interest. In 1871 Wood 1 wrote of a "splenic variety of pseudoleukemia or splenic cachexia" and speculated as to whether there was any consistent change in the bone marrow. He described cases of splenomegaly associated with gelatinous degeneration of the bone marrow. Heuck 2 is credited with an early case report associating generalized osteosclerosis, hepatosplenomegaly, and anemia. In several extensive reviews Sippy * described splenic pseudoleukemia as a condition closely associated with leukemia and having as common findings splenomegaly, anemia, lack of lymphadenopathy, and a slowly progressive course. He described a case of pseudoleukemia with foci of marrow cells surrounded by connective tissue. Later the terms myelosclerosis and osteosclerosis f with aleukemic