In patients with refractory anemia it is important to count and classify the different sideroblasts (intermediate sideroblasts with more than six iron grains or ring sideroblasts), to study the cellularity of the bone marrow and disturbances in thrombo- and myelopoiesis, and to note previous exposure to mutagenic or other toxic agents. Hereditary, primary acquired or secondary acquired ring sideroblastic anemia of the first, toxic type are probably not preleukemic in nature, in contrast to secondary acquired sideroblastic anemia of the second, possibly stem cell type and aregenerative anemias with hypercellular bone marrows and many intermediate sideroblasts.