The amount of new bone produced by grafting genistin in collagen matrix was compared to the bone produced by collagen matrix alone. A total of 18 bone defects (5 mm by 10 mm) were created in the parietal bone of 9 New Zealand White rabbits. Six defects were grafted with genistin mixed with collagen matrix, while 6 were grafted with collagen matrix alone (positive control) and 6 were left empty (negative control). Animals were killed on day 14 and defects were prepared histologically. Quantitative analysis of new bone formation and bone cells was carried out on 100 sections (50 sections for each group) using image analysis. A total of 520 per cent more new bone was present in defects grafted with genistin in collagen matrix than in defects grafted with collagen matrix alone (p less than 0.0001), while no bone was formed in the negative control group. The amount of bone forming osteoblasts was also significantly greater in the genistin group than the positive control group. Therefore, genistin in collagen matrix can increase new bone formation locally in vivo.