Biological regeneration of tissues can be considered a feasible goal in modern medicine largely because of scientific advances in this past decade. These advances clearly demonstrate that the cellular and molecular events taking place during the formation of tissues in embryogenesis are recapitulated during their repair or regeneration. A striking example of this biological principle is bone remodeling and fracture repair, showing a virtually identical cascade of events as seen in the formation of long bones in development. the potential therapeutic implications in diseases such as osteoporosis and osteoarthrosis, in a number of clinical problems such as delayed unions and avascular necrosis and for a large number of congenital osteochondrodysplasias, have intensified the research efforts in the field of skeletal development. This has resulted in major breakthroughs in the characterization of the molecular signals involved in the formation of the skeleton (Erlebacher et al. 1995). An example of this is the discovery of the family of Bone Morphogenetic Proteins (BMPs), originally defined by their ability to induce de novo in an ectopic site endochondral bone formation in vivo (Urist 1965, Wozney et al. 1988, Luyten et al. 1989, Sampath et al. 1990). © 1995 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.