Mycophenolate mofetil (MMF) has been suggested as a promising therapeutic agent in the treatment of idiopathic nephrotic syndrome. Two patients with persistent nephrotic syndrome, secondary to minimal change disease and idiopathic membranous nephropathy, respectively, who were steroid-, cyclophosphamide- and cyclosporine-resistant, were treated with MMF during a 6-12-month period. In these cases there was no beneficial effect from treatment with MMF. Therapy was stopped after 6 months in case 1 and after 12 months in case 2 due to the persistence of proteinuria.