Using both in vivo and in vitro experiments, we have demonstrated that reconstituted collagen will undergo mineralization in a healing bony compartment and that this mineralization is the result of spontaneous precipitation of calcium salts related to the presence of alkaline phosphatase produced by the bone cells. Once calcified, the collagen will undergo cellular resorption by tartrate-resistant multinucleate giant cells similar to osteoclasts. This sequence of events is quite different from that in the suprabony soft tissue compartment, where no calcification of the collagen is apparent, the collagen matrix becomes infiltrated with fibroblast-like cells, and little resorption of the matrix occurs during implantation. It is concluded that reconstituted collagen may be employed as both a tissue barrier, enhancing guided tissue regeneration, and a bone-substitute material that is replaced by natural bone tissue. Thus, materials exhibiting these site-specific reactions are particularly suitable for use in immediate implant placement following tooth extraction. Schlagwörter: bone healing, collagen, guided tissue regeneration, immediate implants