It was shown that colony stimulating factor (CSF) extracted from human urine could increase survival rate obviously and prolonged survival time in irradiated mice. Using tissue culture mini-well plate by means of limiting dilution method, it was shown that with CSF the mature granulocytes in peripheral blood could be kept survival and the counts of them were closely correlated with the concentrations of CSF. With CSF (200 u/ml), in the bone marrow culture the numbers of granulocyte-macrophage colony forming unit (CFU-GM) at the 12th day were larger than that at the 8th day.