Since harmful effects of estrogens in murine lupus are well established, we studied the influence of oral contraceptive therapy on systemic lupus erythematosus activity in 26 female patients with lupus nephropathy. Combined preparations containing either 50 micrograms (14 patients) or 30 micrograms (7 patients) of ethinyl-estradiol were used in 21 courses in 20 patients. Initial manifestations or exacerbations of systemic lupus activity appeared within 3 months of beginning hormonal therapy in 9 patients, an overall incidence of lupus flare-up of 43%; there was major renal involvement in 4 patients. Conversely, evidence of lupus exacerbation did not develop in any of 11 patients who received pure progestogen oral contraceptive therapy with either continuous low-dose norsteroids (6 patients) or discontinuous progestogens at normal dosage (5 patients). These patients were followed for 5--30 months. Our data indicated that oral contraceptive therapy that used estrogens, even at low doses, often induced exacerbation of systemic lupus erythematosus activity. Pure progestogens, which were effective and devoid of such unfavorable effects, may be preferred in these patients.