This study tests the effect of exogenous female hormones on disease activity and severity in women with systemic lupus erythematosus (SLE). Physicians generally do not prescribe hormone replacement therapy (HRT) to women with SLE because of the widely held view that such treatment can activate SLE. This practice is based on the greater incidence of SLE in women than in men, biologic abnormalities of estrogen metabolism, murine models of lupus, several anecdotes of patients having disease flares while receiving exogenous hormones, and a single retrospective study in patients with preexisting renal disease. By contrast, recent retrospective studies suggest that the rate of flare is not significantly increased in patients taking HRT.