Hemopoiesis is the process by which the various blood cell lineages proliferate, differentiate, and mature. Colony stimulating factors (CSFs) are a group of glycoproteins that are extensively involved in hemopoiesis at every level. In recent years, a number of these agents have been identified. They now are being produced in large enough quantities to make possible the in-depth exploration not only of their functions but, more importantly from a clinical perspective, of their therapeutic potential. This article reviews the role of the CSFs in hemopoiesis and summarizes some of the current research concerning their therapeutic applications. In particular, it emphasizes the CSFs involved in granulopoiesis and their uses in hematology/oncology patient populations.