AbstractOsteoinduction by biomaterials has been shown to be a real phenomenon by many investigators in the last decade. The exact mechanism of this phenomenon is, however, still largely unknown. This in vivo study in goats was performed to get insight into processes governing the phenomenon of osteoinduction by biomaterials and had four main goals: (i) to further investigate the influence of physicochemical properties and structure on biomaterial osteoinductive potential, (ii) to investigate the influence of implant size on the amount of induced bone, (iii) to investigate implantation site dependence, and (iv) to investigate changes occurring on the surface of the material after implantation. Intramuscular implantations of four different biphasic calcium phosphate ceramics, consisting of hydroxyapatite and β‐tricalcium phosphate and a carbonated apatite ceramic, indicated that, for a maximal osteoinductive potential, there is an optimal specific surface area for each material type. It was further shown that a decrease of the implant size with a half significantly decreased the relative amount of induced bone. In addition, subcutaneous implantation did not give rise to ectopic bone formation in any of the animals, while bone was induced in most animals intramuscularly. Analysis of the surfaces of the materials after subcutaneous implantation inside diffusion chambers indicated that the increased specific surface area leads to more surface reactivity, which is hypothesized to be essential for osteoinductivity by biomaterials. © 2006 Wiley Periodicals, Inc. J Biomed Master Res, 2006