Freeze‐dried bone allografts have been used in the treatment of periodontal defects for almost a decade. The present study was undertaken to compare the immunogenicity of freeze‐dried cortical bone allografts with fresh cancellous bone and marrow allografts.Cortical bone from a donor baboon was deep frozen and then freeze‐dried. Cancel lous bone and marrow was removed from the same donor.Angular periodontal osseous defects in the jaws of 2 recipient baboons received freeze‐dried osseous allografts and a third animal received fresh marrow allografts. Three months later the animals received a second identical osseous graft in the arch diagonally opposite the first recipient site.Prior to placing the first grafts and 3 weeks after the second graft was in place51Cr release assays were done for cytotoxic antibody and cytotoxic lymphocytes to determine if the osseous allograft materials induced immune responses on the part of the recipient animals.After the second grafts were in place for 3 weeks, the serum and lymphocytes of the animal grafted with allogeneic cancellous bone and marrow showed a higher degree of cytotoxicity for donor target cells than sera and cells from animals grafted with freeze‐dried material.The results indicate that there was little or no immune response, as detected by the assays used, to freeze‐dried cortical bone allografts in comparison to fresh cancellous bone and marrow