The records on 375 consecutive bone marrow aspirations were reviewed to establish the incidence and association of peripheral and bone marrow basophilia. Seventeen cases of peripheral basophilia were identified (4.5 percent incidence) and were associated with iron deficiency (five cases), lung carcinoma (four cases), anemia of undetermined cause (four cases), and chronic myelogenous leukemia, myelodysplasia, chronic renal failure, and acute myelogenous leukemia (one case each). There were six cases of marrow basophilia, including iron-deficiency anemia (two cases), sideroblastic anemia with myelodysplasia, mild dyspoiesis, anemia of chronic disease, and acute erythroleukemia. Marrow basophilia was significantly associated with myelodysplasia and sideroblastic anemia, but was not found in 37 patients with lymphoproliferative disorders. There were no instances of simultaneous marrow and peripheral basophilia. These data support the concept that marrow basophilia is a specific, although not sensitive, marker of disruption of the normal marrow maturation controls.