Bioactive bone growth factors will likely play an important role in the regeneration of bone. BMP-2 is known to promote osteoblastic cell differentiation and osteogenesis. Whether the BMPs act on human osteoblastic cells by increasing immature cell growth and/or differentiation is unknown. The goal of this study was to analyse possible effects of rhBMP-2 on cell differentiation using a human bone marrow cell culture. rhBMP-2 was added to the culture medium once. Fourteen days after addition of rhBMP-2 the cells were incubated with monoclonal antibodies. The cells were counted and analysed in a fluorescence-activating cell sorter (FACS), Compared to the controls there was an increasing effect on granulocytes, B cells and stem cells. The T-cells and monocytes show no increase or decrease after rhBMP-2 treatment.