The megakaryopoietic potential in the bone marrow (BM) of patients in first remission after treatment for acute myelogenous leukaemia (AML) was investigated using long-term bone marrow cultures (LTC) stimulated with megakaryocyte growth and development factor (MGDF). The baseline number of megakaryocyte colony-forming cells (Meg-CFC) was very low. However, there was a 10 to 100-fold increase of Meg-CFC in cultures treated with 10 ng/ml MGDF with mean numbers within the normal range for the first 4 weeks of culture with a 24-fold increase in their cumulative numbers. Similarly, a 12-fold increase in the numbers of megakaryocytes (MKs) was found by CD61 immunostaining. These effects were lost at the dose of 100 ng/ml. In contrast, the cumulative mean numbers of Meg-CFC in the control cultures from normal bone marrow (NBM) were not significantly different from those in cultures treated with 10 or 100 ng/ml MGDF. These results demonstrate that MGDF stimulates megakaryocytopoiesis in patients with AML in first remission, restoring the Meg-CFC compartment to normal values, a result with potential clinical implications for their treatment with autologous transplantation.