90 patients with hemopoietic dysplasia (preleukemia) have been studied with iron kinetics for the mechanism of the anaemia, 23 patients had a bone marrow autoradiography and 18 a bone marrow culture in semi-solid medium. The death was caused in half the cases by acute myeloblastic leukaemia transformation (LAM) and in half the cases by complications of pancytopenia (infection, haemorrhage) or hemochromatosis. Three data give prognostic factors at short or long term: the bone marrow hypoplasia, no patient with major bone marrow hypoplasia (ratio of 59Fe fixation in liver and sacrum of more than 2) lived more than 2 years after the examination. The low labeling index of myeloblasts and promyelocytes, the mean LI is 0.20 patients having lived less than one year after the study and 0.35 for those who lived more than two years. The bone marrow culture of the macroclusters type, no patient whose bone marrow grew with macroclusters and no colonies survived more than 8 months after the study. These three data seem to be essential in the regular survey of the patients with hemopoïetic dysplasia.