Due to the immunopharmacological profile of the recombinant IL-1 receptor (IL-1-R) and its potential to modulate biological activity in various inflammatory autoimmune disease models, we further elucidated its disease modifying activity on the development of a systemic lupus erythematosus (SLE)-like disease in BDF1 hybrid mice and in MRL/lpr autoimmune mice. Treatment of BDF1 mice with the IL-1-R during the induction phase resulted in a strong inhibition of the development of a glomerulonephritis, prolonged the survival time and improved the survival rate. Even a therapeutic effect was demonstrated when this receptor was given after the appearance of clinical symptoms. Treating MRL/lpr mice, which develop spontaneously a SLE-like disease, with the IL-1-R resulted in an inhibition of the developing glomerulonephritis and splenomegaly, in a reduction of swollen lymph nodes and in a decrease of autoantibody formation. Even in the established autoimmune disease of MRL/1 pr mice the IL-1-R reduced proteinuria, the levels of autoantibodies and also improved the survival rate.