Recombinant human bone morphogenetic protein-2 (rhBMP-2) and basic fibroblast growth factor (bFGF) are the focus of research pertaining to the stimulation of bone formation. We ascertained the effects of different concentrations rhBMP-2 on proliferation and differentiation of bone marrow stromal cells (BMSCs) in vitro and on ectopic bone formation in rats. BMSCs were obtained from beagle dogs and cultured in medium containing different concentrations rhBMP-2 and bFGF (0, 25, 50, 100, or 200 ng/mL). In a separate experiment, BMSCs were treated with different ratios (1:1, 2:1, 4:1, or 8:1) of rhBMP to bFGF (in each case the concentration of rhBMP was 100 ng/mL and the bFGF concentrations 100, 50, 25, or 12.5 ng/mL). Proliferation and differentiation of BMSCs were quantified by assessing methyl thiazole tetrazolium (MTT) and alkaline phosphatase (ALP) over 6 consecutive days. Von Kossa staining was performed on day 6. For the in vivo tests, porous calcium phosphate cement (CPC) was seeded with BMSCs (5 x 10(4)) in medium containing 100 ng/mL rhBMP-2, 50 ng/mL bFGF or combined 100 ng/mL rhBMP-2 and 50 ng/mL bFGF. These cells were then subcutaneously implanted in four sites in nude rats. Bone formation was detected by histology at weeks 4 and 12 and quantified using a KS400 computer based image analysis system. It was determined that combined rhBMP-2 and bFGF at a ratio of 2:1 (100:50 ng/mL) promoted significantly increased BMSC proliferation and differentiation of BMSCs compared to rhBMP-2 or bFGF alone (p < 0.05). CPC with combined 100 ng/mL rhBMP-2 and 50 ng/mL bFGF stimulated more bone formation than either 100 ng/mL rhBMP-2 or 100 ng/mL bFGF (p < 0.05). These results show that a combination of rhBMP-2 and bFGF effectively induces early BMSC proliferation and differentiation in vitro. When combined, rhBMP-2 and bFGF synergistically promote new bone formation.