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Radiographic and histological studies of sixteen massive retrieved human allografts were carried out after the allografts had been in situ for four to sixty-five months. The studies demonstrated that union between the allograft and the host took place slowly at cortical-cortical junctions by the formation of an external callus derived from the cortex of the host, and it took place more rapidly at cancellous-cancellous junctions by internal callus advancing from the host into the allograft. Internal repair took place very slowly, was confined to the superficial surface and the ends of the graft, and had involved only 20 per cent of the graft by five years. The deep unrepaired portions of the graft retained their architecture, and where bone cement had been used to fix a prosthetic stem or an intramedullary rod to the allograft, there was no evidence of resorption of bone or loosening of the device. Soft tissues of the host became attached to the graft by deposition of a thin seam of new bone on the surface of the graft. A previous fracture of two grafts had healed before the time of retrieval. Analysis of the articular cartilage revealed no evidence that any chondrocytes had survived, even when the graft had been cryoprotected before it was preserved by freezing. The necrotic cartilage functioned well for as long as five years, and as it degenerated, it was covered by a pannus of fibrovascular reparative tissue. Two allografts that had been removed because of rejection were surrounded by an envelope of chronic inflammatory tissue that prevented union, adherence of soft tissue, and internal repair. Internal repair was more advanced about sites of fracture and adjacent to recurrent tumors than in other portions of the graft. These findings suggest that large frozen allografts in humans are osteoconductive rather than osteoinductive.