An acid-modified arabinogalactan protein composition, having an arabinose-galactaose ratio of less than 3.5:1, comprising 5-10% Rha, 20-35% Gal, and less than 5% Glc, prepared from Astragalus membranaceus, is useful for treating a number of conditions. For example, an acid-modified arabinogalactan protein composition having features of the invention is useful for stimulating hematopolesis, inducing the proliferation of megakaryocytes, inducing the maturation of megakaryocytes, and stimulating the production of IL-1, IL-6, TNF-, IFN-, GM-CSF, G-CSF, and neutrophils, and stimulating the action of neutrophils; stimulating the immune and/or hematopoietic system of a mammal suffering from neutropenia, anemia, thrombocytopenia, exposure to cytotoxic agents, exposure to radiation, cachexia, emesis, and drug withdrawal symptoms; and is effective to restore the immune response to infection, in immunosuppressive conditions, and to protect hepatic cells in hepatitis B.