Dog leukocyte antigen (DLA)-matched and mismatched, fresh and frozen (cryopreserved) osteochondral allografts of the proximal part of the radius were implanted orthotopically in beagles. The systemic and local (intra-articular) immune responses were monitored for eleven months using a 51chromium release assay with donor peripheral-blood lymphocytes as target cells. DLA-mismatched fresh grafts markedly and persistently stimulated the formation of antibody directed against donor cell-surface antigens, while DLA-matched grafts did not elicit systemically detectable antibody. The same general pattern was noted when antibody-dependent cell-mediated cytotoxicity was assayed. There was measurable cell-mediated immunity to donor cells from six weeks after surgery onward, although no distinct pattern or differences between experimental groups were noted. Higher titers of anti-DLA antibody were found in synovial fluid than in serum; in fact, synovial antibody was detectable when systemic antibody was not. Joints that received DLA-mismatched grafts had the highest titer of antibody and the intra-articular response was significantly reduced when the graft had been frozen.