TISSUE GRAFTING from a genetically dissimilar donor of the same species will generally incite an immunologic response resulting in rejection of the allograft. While homoviable grafts are most often rejected, some homostatic grafts are eventually replaced by living elements of the recipients. These include cortical bone, 1 blood vessels 2 and cornea. 3Assuming that all successful grafts are ultimately replaced by host tissue, it seems reasonable to question the possible fate of a viable allograft consisting of bone and marrow in a periodontal lesion. Would such a graft elicit antibody formation sufficient to cause rejection within a short period of time, or would rejection occur slowly, permitting progressive resorption and repair with eventual replacement of the graft with formed bone?To answer this question, a periodontal bone and marrow grafting experiment was designed to compare host response in animals receiving an immunosuppressant drug, which will decrease reactivity to antigens, and the