This in vivo study compared the regenerative processes within defined defects of the porcine skull after delivery of a porous algae-derived hydroxyapatite (adHA), a similar, experimental adHA carrying the cell binding peptide P-15, used solely and in combination with 25% autogenous bone (AB). Particulated AB served as a control group. During an observation period of 26 weeks, microradiography and histology were performed at four specific times. Significantly higher mineralization rates (p = 0.008) were found 4 weeks after application of the bioactive material in combination with AB. At 12 weeks there was a significantly higher mineralization (p = 0.036) following the application of the bioactive form alone. This study showed significantly higher mineralization after use of a P-15 bioactivated material at early stages. Thus, it can be concluded that the application of the P-15 sequence to an hydroxyapatite accelerates the process of early bone formation, whereas no long-term effect was traced. (c) 2005 Elsevier Inc. All rights reserved.