We have conducted a controlled trial on the efficacy of cyclosporine in eight patients with steroid-resistant nephrotic syndrome (four with idiopathic minimal lesion nephrotic syndrome and four with focal segmental glomerulosclerosis). Patients were randomly allocated to a cyclosporine (5 mg/kg/d) or a control group. After eight weeks of therapy and one month without cyclosporine therapy, patients in the control group were given cyclosporine for eight weeks and those in the cyclosporine group became controls. Before the initiation of treatment, there was no difference between the groups with regard to proteinuria and serum albumin levels. Proteinuria remained unchanged in the cyclosporine group, while there was a significant increase in proteinuria in the control group. There were no significant changes in serum albumin levels in either group during the trial. This study does not support the use of cyclosporine at the dose of 5 mg/kg/d in patients with steroid-resistant minimal lesion nephrotic syndrome or focal segmental glomerulosclerosis.