We analyzed the maintenance of acute myeloid leukemia clonogenic cells (AML CFU-L) in liquid culture in the presence of five potential differentiation inducers: trans-retinoic acid, 1,25-dihydroxy vitamin D3, interferon gamma, granulocyte colony-stimulating factor (G-CSF), macrophage colony-stimulating factor (M-CSF), used singly and with two combined. The culture medium contained either fetal bovine or human serum from normal donors. CFU-L recovery after 7 days was compared to that observed in control cultures. Of AML cases and HL60 cells, 11/15 displayed greater than 50% CFU-L reduction in response to one or more inducers. In 8/9 responsive cases that underwent the nitroblue tetrazolium (NBT) reduction test, an increase in the percentage of functionally mature (NBT-positive) cells was detected. The combination of retinoic acid with interferon gamma was most effective in reducing CFU-L recovering (8 responsive/15 AML cases), G-CSF and M-CSF displayed either inhibitory or stimulatory activity in different AML cases. The type of serum employed generally did not affect the response to inducers of differentiation. No significant inhibition of the recovery of granulocyte-macrophage colony-forming units was determined by the five inducers in experiments with three normal bone marrow samples. Our experiments indicate that biological differentiation inducers can reduce AML CFU-L self-renewal and increase the proportion of differentiated cells at concentrations that do not affect normal myelopoiesis and could be achieved during treatments in vivo.