We report a prospective randomized study of 39 patients with systemic lupus erythematosus and progressive glomerulonephritis who were assigned to treatment groups that received either prednisone alone or prednisone and cyclophosphamide combined. They received treatment for 6 months and were then followed up for an additional 18 months. No difference in outcome was seen in the two groups at the end of 6 months. Among patients followed up for an average of 24 months, fewer individuals showed later renal progression among those treated with cyclophosphamide and prednisone than among the group treated with prednisone alone.