We have investigated the effects of different growth factors on the proliferation and osteogenic potential of primary cultures of human bone marrow stromal cells (BMSC). Fibroblast growth factor (FGF)-2 was the most effective in promoting growth of these cells in vitro. The size of colonies formed in clonal conditions was approximately 2.5 times larger in presence of FGF-2. Also the morphology of BMSC was affected: cells cultured in 10% FCS alone became flattened, whereas FGF-2 expanded cells maintained a fibroblast-like elongated phenotype. Levels of alkaline phosphatase activity in BMSC expanded with FGF-2 were significantly lower (56%) than control and, after stimulation with ascorbic acid, betaGlycerophosphate and dexamethasone, FGF-2 expanded BMSC deposited approximately 3-fold more mineralized matrix than control cells. We have assessed osteogenicity of BMSC on hydroxyapatite porous scaffolds (bioceramics) by an ectopic bone formation assay. FGF-2 expanded BMSC yielded a higher bone formation (>20-fold) than control cells. We conclude that FGF-2, promoting BMSC proliferation, maintains cells in a more immature state allowing in vitro expansion of human osteo-progenitors which, associated with bioceramics, can differentiate in vivo and form bone tissue.