TUBERCULOSIS has been associated with a variety of hematological abnormalities. These include hypoplasia of the bone marrow,1,2 myelofibrosis,3-5 and polycythemia.6 Tuberculosis is sometimes associated with a leukemoid reaction which must be differentiated from leukemia. In 1911 Coley and Ewing,7 from postmortem studies, first drew attention to the leukemoid response which may be evoked by tuberculosis. The association was first made antemortem by Mills and Townsend 8 in 1937. We have found only 38 reports of patients who had leukemoid reactions to tuberculosis which fulfilled the following criteria: (1) tubercle bacilli had to be demonstrated and (2) an excessive leukocytosis or an abnormal shift towards immaturity in the peripheral blood or in the bone marrow. A diagnosis of leukemia was considered to be excluded if a lasting hematologic recovery occurred or if visceral infiltration with leukocytes could not be demonstrated at autopsy. It is the purpose of this paper to discuss