New Zealand mice develop autoimmune disease usually accompanied by glomerulonephritis. A graft-versus-host reaction was induced in New Zealand Black X New Zealand White F1 hybrid mice by administration of New Zealand White spleen cells. The mice so treated had diminished antibody responses to both an exogenous antigen (sheep red blood cells) and an endogenous antigen (native DNA). They had much less glomerulonephritis and increased survival times compared to unmanipulated controls, apparently due to immunosuppression. Similar hybrid mice treated with high doses of cyclophosphamide (70mg/kg/week) were more immunosuppressed than mice with graft-versus-host reactions and had even greater survival times.