We studied the relative role of gp70-antigp70 complexes in the pathogenesis of murine lupus nephritis, and we used as an index of its contribution, the association between attenuation, or progression, of renal disease and decrease or increase in concentration of gp70 complexes and IgG in the plasma and renal eluate of NZB/W mice. The arrest or attenuation of nephritis, by immunosuppression, was associated with decreased concentrations in the plasma and renal eluates of IgG and gp70 complexes, and the relative concentration of these reagents in the eluates better reflected the extent of renal disease than did their concentration in the plasma. Neither the relative concentration of Clq-reactive materials, nor the quantity of antiDNA antibodies in the plasma, distinguished the mice whose nephritis was arrested by immunosuppression from those with terminal renal failure. The findings further support that the gp70-antigp70 system plays an important role in the pathogenesis of murine lupus nephritis.