AbstractThe serum titer of colony‐stimulating factor which stimulatesin vitrogrowth of bone marrow cells to form colonies of granulocytic and mononuclear cells is elevated 18 hr following bilateral ureteral ligation and unilateral or bilateral nephrectomy in mice. Following unilateral ureteral ligation, there is a moderate elevation of colony‐stimulating activity at 3 and 7 days. These results suggest that the titer of serum colony‐stimulating factor is dependent in part on renal clearance of the f