The mechanisms by which interferon-α (IFN-α) restores normal hematopoiesis in chronic myelogenous leukemia (CML) are not well understood. We have recently demonstrated that IFN-α acts directly on CML hematopoietic progenitors to restore their adhesion to marrow stroma by modulating β1 integrin receptor function. In the present study we examined the effect of IFN-α treatment of marrow stroma on subsequent adhesion of CML progenitors. Stromal layers were preincubated with IFN-α (10,000 μm/ml) for 48 h. Subsequent coincubation, with CML progenitors for 2 h resulted in significantly increased adhesion of CML progenitors. We demonstrated that α4β1 and α5β1 integrin receptors were involved in the enhanced adhesion of CML progenitors, suggesting that IFN-α-treated stroma can upregulate CML integrin function. This effect is due, at least in part, to IFN-α-induced increased stromal production of the chemokine macrophage inflammatory protein-1α (MIP-1α), which upregulates β1 integrin-dependent adhesion of CML progenitors to stroma. Thus, IFN-α treatment of marrow stroma restores β1 integrin-dependent adhesion of CML progenitors, at least in part through induction of MIP-1α production. These observations provide further insights into mechanisms by which IFN-α may restore normal hematopoiesis in CML. (J. Clin. Invest. 1995. 96:931-939.) Key words: chronic myelogenous leukemia hematopoiesis interferon-α integrins macrophage inflammatory protein-1α.