Autoimmune-prone BXSB male mice were supralethally irradiated and transplanted with CBA/H bone marrow cells. A complete and long-term chimerism was established when donor mice had been induced to develop tolerance of BXSB male antigens by combined treatment with BXSB male spleen cells and cyclophosphamide. Such chimeras did not express autoimmune phenomena or develop lethal autoimmune manifestations. Nor did the recipient mice develop the wasting syndrome or evidence of persistent immunodeficiencies that have been seen in other strains of autoimmune-resistant mice that had been transplanted with bone marrow cells across major histocompatibility complex barriers following an initial purging of the bone marrow of Thy-1+ cells using anti-Thy-1+C.