This is a study of the correlation between the age of animals and the osteogenic potential of free periosteal autograft. The tibial periosteum of 27 rabbits, ranging in age from 4-104 weeks, was stripped and implanted into the quadriceps. Radiographic and histologic examination demonstrated that new bone was formed in both the young and adult rabbits. The morphologic basis and mechanism of bone formation of periosteum are discussed. Maintenance of integrity of the cambium layer of the periosteal graft is emphasized. Free periosteal graft of adult rabbits in the "resting" state can retain its osteogenic potential and produce new bone.