Myelopoietic cell proliferation in granulocytopenia of refractory anaemia and preleukaemic states with hyper-plastic bone marrow

Summary Myelopoiesis in healthy subjects and in 8 cases of refractory anaemia or preleukaemic states was studied by the combined cytophotometric-autoradiographic method. Granulocytopenia was present in 7 of 8 cases. The results can be summarized as follows: 1. Mature myelocytes of healthy persons are a mainly differentiating cell population with a low labelling index (3–10%) and a high incidence in G₁-Phase. 2. The proliferating immature granulopoietic cells of the patients with neutropenia showed a reduced labelling index with³H-thymidine as a result of an arrest of these cells in G₁ (6 of 8 cases). 3. A similar result was obtained in the study of the hyperplastic myelopoiesis of an other patient with preleukaemia and normal granulocyte count in peripheral blood, with the disturbance of cell proliferation preceding the symptom neutropenia. 4. Finally in only one case an increased frequency of myelopoietic cells in G₂-phase was found suggesting an arrest of cell proliferation in the premitotic phase.We wish to thank Miss Broszies for her excellent technical assistance.