From 1969 to 1975, 53 patients with lupus nephritis took part in randomized trials comparing prednisone, oral azathioprine plus low-dose prednisone, and oral cyclophosphamide plus low-dose prednisone. After a mean follow-up of 85 months, cyclophosphamide appears marginally superior to prednisone for maintaining renal function (p = 0.03) and preventing end-stage renal failure (p = 0.07). Chronic change shown by renal biopsy assessed by a chronicity index was found useful in predicting renal function outcomes and response to immunosuppressive therapy. Three of 21 patients with a low chronicity index and 9 of 10 patients with a high chronicity index doubled their serum creatinine (p less than 0.00003). The probability of renal functional deterioration was not different among the treatments studied. However, in 14 patients with an intermediate chronicity index, 1 of 11 patients treated with azathioprine or cyclophosphamide doubled the serum creatinine level whereas all 3 patients treated with prednisone have progressed to end-stage renal failure (p = 0.005). The study suggests that single-drug oral immunosuppressive treatment combined with prednisone is most beneficial in lupus patients with intermediate chronic change shown by renal biopsy.