AbstractA soluble form of the reticuloendothelial- and immune modulating agent glucan (glucan-F) has been evaluated for its effects on hanopoiesis. A single 5.0 mg intravenous injection of glucan-F into C3H/HeN mice increased peripheral white blood cellularity, bone marrow and splenic cellularity, bone marrow and splenic granulocyte-macrophage progenitor cell numbers (GM-CFC), and splenic pluripotent stem cell (CFU-s) and erythroid progenitor cell (CFU-e) numbers. Serum levels of granulocytemacrophage colony stimulating activity (CSA) were also elevated following glucan-F administration. These hemopoietic responses correlate well with those previously shown to be induced by intravenous administration of particulate glucan (glucan-P). In contrast to glucan-P, however, intravenous glucan-F administration has been shown not to induce granuloma formation and severe hepatosplenomegaly, thus the potential clinical use of glucan-F as a hemopoietic stimulant is more likely than that of glucan-P.