Acute leukaemia blast cells fail to mature into terminally differentiated cells and accumulate in the haemopoietic tissues. In analogy with normal haemopoiesis, the leukaemic mass is largely non-dividing and descends from a small pool of leukaemic progenitor cells with high proliferative activity. In vitro culture methods have become powerful instruments to analyse human leukaemia progenitor cells. These techniques have in recent years been considerably improved as the result of the availability of the recombinant HGFs. Here we have summarized the current insights in the growth properties of acute leukaemia progenitor cells, derived from the application of fully defined in vitro assays. We have discussed the proliferation and maturation abilities in relation to cytogenetic abnormalities, status of growth factor receptors and the property of autocrine growth stimulation and evaluated the significance of these findings for the understanding of the pathogenesis of acute myeloblastic leukaemia and acute lymphoblastic leukaemia.