This study is designed to explore the use of myfortic ® in patients with active lupus erythematosus. Similar drugs in this class are increasingly used in organ transplantation and in autoimmune diseases. With the established safety profile of myfortic ® in allo-transplantation and the already existing data of mycophenolate mofetil in autoimmune diseases, this study should help to demonstrate the beneficial effect of myfortic ® on lupus activity. The aim of the study will be to show a decreased disease activity with myfortic ® compared to standard maintenance therapy with azathioprine.