There is disclosed a process for the mineralization of collagen fibers whereby collagen fibers formed from collagen are contacted with a solution of calcium and phosphate ions under conditions to effect nucleation and in-vitro growth of mineral crystals within and on the surface of the collagen fibers to form intact collagen fibers with subfibrillar substructure and wherein preparations of such mineralized collagen fibers are used in bone replacement therapy as well as to induce repair in bony defects.