Recruitment of quiescent, clonogenic blasts from patients with acute myeloid leukemia (AML) by hematopoietic growth factors (HGFs) may improve the cytotoxic effects of cell-cycle-specific drugs like cytosine-arabinoside (Ara-C). Using the culture methods described by Nara and McCulloch and making a distinction between self-renewing and post-deterministic mitoses, we analyzed the effects of stem cell factor (SCF), a growth factor acting on early hematopoietic progenitor and stem cells. First, we demonstrated that SCF, used in combination with other HGFs included in fetal calf serum (FCS) and/or in 5637 cell line supernatant (5637-CM), stimulated both colony formation and self-renewal of blast progenitors from 10 patients, unlike SCF alone. We tested the effects of SCF on the recruitment of cells in the S-phase by using a bromodeoxyuridine/DNA (BrdUrd/DNA) staining method in flow cytometry (FCM). We showed that SCF stimulated proliferation of AML cells significantly in 9/18 patients with AML. Second, we tested the influence of SCF on the sensitivity to Ara-C of self-renewing leukemic cells from 18 patients with AML. We showed that SCF was efficient in increasing the toxicity of Ara-C on the self-renewing blast progenitors, especially with high concentrations of Ara-C. However, a large patient-to-patient heterogeneity was found and the activity of SCF was not correlated with its effect on the cell cycle. These data indicate that SCF can enhance sensitivity to Ara-C of some leukemic cells with self-renewing capacity.