The effect of short-term immunosuppressive treatment with antithymocyte serum-procarbazine (ATS-PCH) and cyclosporin-A (Cy-A) on survival of allogeneic rib chondrocyte grafts was examined morphologically and by evaluation of specific humoral and cellular antigraft immunity. The latter were evaluated by means of leukoagglutination and the indirect migration inhibition assay, respectively. Untreated recipients of syngeneic rib chondrocytes and untreated recipients of whole syngeneic and allogeneic rib cartilage served as controls. Transplanted syngenic rib chondrocytes formed cartilaginous nodules similar to rib cartilage in situ. These nodules contained hypertrophied chondrocytes, but neither physiologic resorption by vascularized connective tissue nor bone formation occurred after an observation period of longer than six weeks. Transplantation of allogeneic chondrocytes resulted in development of humoral and cellular antigraft immunity, and the formed cartilage was destroyed by infiltrating immune cells. Immunosuppression by ATS-PCH resulted in inhibition of graft destruction and a marked decrease of specific humoral antigraft immunity. Cellular antigraft immunity did not occur. Moreover, neither the histologic appearance of the cartilaginous nodules nor the results of immunologic response evaluations in the ATS-PCH-treated group differed from those in untreated whole allogeneic cartilage recipients. Treatment with Cy-A did not significantly improve survival cartilage formed by allogeneic chondrocytes.