Basic fibroblast growth factor (bFGF or FGF-2) is an angiogenic and pleiotropic factor involved in the proliferation and differentiation of numerous cell types. It is expressed mostly in tissues of mesoderm and neuroectoderm origin, and plays an important role in the mesoderm induction, together with transforming growth factor-beta (TGF-beta). Although hematopoietic cells derive from the mesoderm, relatively few studies have addressed the role of bFGF in the hematopoietic system until recently. It appears that bFGF is expressed and produced by bone marrow stromal cells, as well as by cells from several mature peripheral blood lineages. It is released and stored in the bone marrow extra-cellular matrix. FGF-receptors (FGF-Rs) are expressed on nearly every cell of hematopoietic origin tested so far. Growing evidence shows that bFGF can positively regulate hematopoiesis, by acting on various cellular targets: stromal cells, early and committed hematopoietic progenitors, and possibly some mature blood cells. It synergizes with hematopoietic cytokines, or antagonizes the negative regulatory effects of another factor, TGF-beta, thus potentially playing a central role in hematopoiesis.