Colony-stimulating factors may be multilineage or lin-eage restricted. Lineage-restricted CSFs generally are late acting, whereas multilineage CSFs tend to act on cells earlier in the differentiation pathway. Figure 1 identifies the association of these CSFs in the process of hematopoiesis. Known multilineage CSFs include interleukin-3 (IL-3) and GM-CSF. Lineage-restricted CSFs include G-CSF, M-CSF, TPO, and EPO.