AbstractThe incorporation of tritiated thymidine into the DNA of murine bone marrow cells could be stimulated by fraction PH-I Ba separated from the roots ofPseudostellaria heterophyllain a dose-dependent mannerin vitro. Moreover, PH-I Ba could induce the differentiation of murine bone marrow cells from pluripotent haemopoietic stem cells into macrophages-like cellsin vitro. Autocrine or paracrine stimulation of granulocyte-macrophage colony stimulating factor was likely to underly the induction of differentiation. Therefore, PH-I Ba was proved to be an immunostimulating agent for mouse marrow hematopoiesis and was found to be a polysaccharide. The sugar components were analyzed by Gas Liquid Chromatography of their alditol acetates.