Abstract
Myelopoiesis has been studied using quantitative cytochemical, cytometric and autoradiographic techniques. The earlier speculation that normal small myelocytes were mainly in Gt and early S has been confirmed. The distribution of promyelocytes and myelocytes between the different stages of interphase was normal in β-thalassaemia major and acquired sideroblastic anaemia; the disturbance in cell proliferation in these disorders being confined to erythropoiesis. The mean labelling index of promyelocytes and myelocytes in patients with a reactive neutrophil leucocytosis was 15% higher than the mean for normal marrow, indicating a significant increase in proliferation. Myelocyte labelling indices above 50% were seen in megaloblastic haemopoiesis due to vitamin B12 and folate deficiency and were rarely encountered in other diseases.