Stimulation of murine bone-marrow colony formation by conditioned medium from human fetal liver cells

A substance that stimulates growth of colonies of mononuclear granulocytic cells derived from the bone marrow of mice was produced by incubating fetal liver cells (conditioned medium). This substance appears to have the same properties described elsewhere as colony-stimulating factor (CSF). The enhanced stimulatory ability of the conditioned medium from human fetal liver cells compared to medium not conditioned suggests that fetal liver is a potent source of colony-stimulating factor.