The cases of twenty-six patients who received a massive allotransplant of frozen bone, with a known degree of histocompatibility between the donor and the recipient, were studied. Twenty-two patients were followed for more than two years (range, twenty-four to ninety-two months). Twenty-three biopsies were performed in sixteen patients from nine to seventy-eight months after transplantation. No clear relationship could be established between the degree of histocompatibility of the donor and the recipient and the incorporation of the graft, probably in part due to the number of variables involved and the polymorphism of the HLA system. However, no early massive resorption of the transplant was seen in this series, in which, by the design of the protocol, no recipients had pre-existing circulating antibodies to the antigens of the donor. Two allografts showed infiltration by round cells and vascular lesions in the absence of infection, which is suggestive of an immune response against antigens from the donor. Both matched poorly with the donor for HLA antigens. The individual who had the strongest reaction was the only recipient in the series who had a massive failure of the transplant.