Effects of a single injection of PEG-rHuMGDF on the expansion of bone marrow cells capable of surviving in lethally irradiated mice. One hour after irradiation at a dose of 3.5 Gy, mice were intravenously given 80 μg/kg PEG-rHuMGDF (•) or vehicle (○). Two days later, the mice were killed and their bone marrow cells (10⁶ cells per mouse) were intravenously injected into syngeneic recipient mice that had been lethally irradiated at a dose of 8.5 Gy. One group of lethally irradiated mice received no transplantation of bone marrow cells (□).