This is a phase 2 trial to evaluate the effectiveness and toxicity of immunosuppressive drug therapy in patients with membranous lupus nephropathy over a 12 month study period. Patients with renal biopsy documented membranous nephropathy will all be treated with alternate day prednisone and will be randomized to receive: a) no additional therapy (control group), b) intravenous cyclophosphamide up to 1.0 gm per m(2) body surface area every other month for 6 total doses, or c) oral cyclosporin A up to 200 mg per m(2) body surface area daily for a total of 11 months. Patients with glomerular filtration rates 25-66 ml/min will be randomized only to prednisone alone or to prednisone plus cyclophosphamide. Renal function and disease activity will be monitored throughout the study; physiologic measures of glomerular function (GFR, permselectivity) will be examined at study entry and at the conclusion of the study. Comparison will be made of the number of favorable outcomes of glomerular function as well as drug related toxicities achieved by each treatment group at the end of the 12th study month.