Adoptive immunotherapy with transfusion of donor lymphocytes in allogeneic stem cell chimeras has been successful in the treatment of recurrent chronic myelogenous leukaemia (CML) and some patients with acute myeloid leukaemia (AML). The hypothesis that the graft-vs-leukaemia effect (GVL) is promoted by leukaemia-derived dendritic cells has been supported by the concurrent treatment of patients with cytokines that are known to induce differentiation of leukaemia cells towards dendritic cells. In combination with donor lymphocyte transfusions, treatment with interferon-alpha and granulocyte-macrophage colony-stimulating factor has been studied in patients with recurrent CML and AML, and pre-emptively in patients with high-risk AML. Long-term remissions have been observed in cytokine-treated patients, indicating the beneficial effect of cytokine stimulation of GVL reactions. This is likely to be due to differentiation of leukaemia progenitor cells towards dendritic cells in vivo.