To determine how low intensity pulsed ultrasound alters gene expression in rat bone marrow stromal cells and to see if combining this stimulation with BMP-2, cells were pre-cultured for eight days in the presence of 50 microg/ml ascorbic acid and then exposed to either low intensity US or 100 ng/ml BMP-2 or both combined, beginning on the first, third fifth or seventh day of culture so that cells were exposed to the stimuli for one, three, five or seven days. Real time PCR was used to determine the effect of these treatments on gene expression of several genes associated with osteogenesis. The expression of some of the genes (Cbfa-1/Runx2, IGF-receptor, Alk-3, alkaline phosphatase, osteopontin, TGF-beta1, BMP-7) was increased compared to untreated controls. Combination of US and BMP-2 treatment did not lead to synergy of the two stimuli. Cbfa-1 stimulation occurred more quickly with US than with BMP-2. Increases in gene expression were greatest after 3 days exposure to US, with similar results for BMP-2 treatment implying that there may be a time dependence for the stimulus of osteogenic gene expression in stromal cells.