In this comparative open-label cohort study, the investigators compared the efficacy and safety of tacrolimus (TAC)and cyclophosphamide (CYC) in the treatment of diffuse proliferative and membranous lupus nephritis with severe renal disease. Treatment of lupus nephritis (LN) with cyclophosphamide is effective, but retain a certain proportion of renal function exacerbations. Tacrolimus may be a suitable substitute treatment for CYC.