AbstractA bioactive and resorbable scaffold is necessary to exhibit the osteoinductive potency of recombinant human bone morphogenetic protein‐2 (rhBMP‐2). In a previous study, we found that synthetic octacalcium phosphate (OCP) enhances bone regeneration and is replaced by newly formed bone after it is resorbed. We hypothesized that OCP may be useful as an effective scaffold for rhBMP‐2 to enhance bone regeneration. To test this hypothesis, the present study was designed to investigate whether an OCP/BMP composite implant could more effectively enhance bone regeneration. A critical‐sized defect was made in a rat calvarium and 1. 15 mg of OCP combined with 10 μg of rhBMP‐2 (OCP/BMP 10 μg), 2. 15 mg of OCP combined with 1 μg of rhBMP‐2 (OCP/BMP 1 μg), or 3. OCP (OCP alone) was implanted into the defect and fixed at 4 or 8 weeks after implantation. The percentage of newly formed bone (n‐Bone%) in the defect was determined by a histomorphometrical analysis. A statistical analysis showed that n‐Bone% with OCP/BMP was significantly higher than that with OCP at both time points, whereas the difference in n‐Bone% between OCP/BMP 10 μg and OCP/BMP 1 μg was not significant. The present results suggest that OCP can be used as an effective scaffold for rhBMP‐2 and this OCP delivery system may be able to reduce the standard effective dose of rhBMP‐2, which would be beneficial because low doses (<100 μg/g OCP) of rhBMP‐2 enhance bone regeneration. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 71A: 299–307, 2004