Acidic isoferritins (AIF) known as negative regulators of normal bone marrow cells (CFU-GM) failed to inhibit the induction of differentiation and growth of M1 cells. AIF stimulates differentiation of normal granulomonocytic progenitors. AIF has been studied as a tumor associated-antigen for its potential clinical value, and monoclonal antibodies against AIF have been developed for the serum AIF detection and tumor localization.