The role of mineralization was studied in an experimental model of osteoinduction consisting of the implant of decalcified bone matrix in the rat muscle. After vascular connective tissue invasion of the matrix, the first phenomena is the appearance of hydroxyapatite crystals in the area of chondroid metaplasia from where the deposit of calcium-phosphate is extended to the surrounding decalcified matrix. The recalcified areas act as a substratum for the neo-osteogenesis. The appearances observed reproduced those of enchondral ossification, where the first osteoblasts differentiated on the calcified cartilaginous matrix and began to supply new bone matrix. Non-decalcified bone matrix implants were surrounded by a connective tissue capsule with features identical to those of a foreign body reaction and with total absence of vascular invasion. The absence of induction in this type of implant may be related either to masking of the osteoinducing protein in the calcified matrix, or to the absence of cells with osteogenic differentiation potential due to the lack of cellular invasion of the implant.