Recombinant murine granulocyte macrophage colony-stimulating factor (rGM-CSF) has been produced in Escherichia coli and purified to homogeneity. GM-CSF has an established role as an in vitro regulator of granulocyte and macrophage colony formation. We have determined that rGM-CSF also has intrinsic activity as a megakaryocyte colony-stimulating factor and that rGM-CSF augments the effect of int...