The murine diploid hematopoietic cell line 32D Cl3 strictly requires interleukin-3 (IL-3) for proliferation. When 32D Cl3 cells are transferred to IL-3-free medium which contains recombinant human granulocyte colony stimulating factor (rhG-CSF), the cell number increases four- to five-fold, and after 14 days the whole cell population is differentiated into morphologically normal and myeloperoxidase- and lactoferrin-positive metamyelocytes and granulocytes. Infection with Abelson murine leukemia virus (A-MuLV) of 32D Cl3 cells growing in the presence of IL-3 induces, within 2 weeks, the appearance of cells that are IL-3-independent for growth. The latter cells lack myeloid, T and B cell markers, and are unable to differentiate, even in the presence of very high doses of rhG-CSF. However, once the 32D Cl3 cells have been exposed to G-CSF, they become resistant to the transforming effects of A-MuLV as judged by the appearance of the IL-3-independent clones. These findings suggest that the ability of Abelson virus to transform immature progenitor cells is due to interference of the v-abl gene product with the mechanisms that control the commitment of the cells to differentiate.