Captopril, an angiotensin-converting enzyme inhibitor, was used to treat 14 patients with lupus nephritis and severe hypertension. All patients had reduced renal function and were on regular immunosuppressive therapy with corticosteroids and azathioprine. The initial dosage of captopril was reduced according to the level of renal impairment. 11 patients were treated for more than 6 months. Excellent blood pressure control was achieved with captopril, from a mean of 178 +/- 7/110 +/- 4 to 145 +/- 5/92 +/- 3 mm Hg at 6 months, usually in combination with a diuretic only. In 5 cases, a beta-blocker was added. In 3 patients, captopril therapy was discontinued within the 1st month of treatment. 1 patient did not respond to captopril at all; 1 patient had a rejection crisis and required dialysis; in 1 case, a general exanthema developed within 3 weeks and captopril medication was stopped. In addition to blood pressure control, renal function improved in 7 of the long-term-treated patients (mean increase in glomerular filtration rate 73 +/- 34%). In 3 patients, a continued slow deterioration renal function occurred, and in 1 patient, renal function remained unchanged. It is concluded that captopril is an effective antihypertensive drug in patients with systemic lupus erythematosus (SLE). Captopril treatment increased renal function in 64% of patients on long-term therapy. Not only optimal blood pressure control but other factors may also contribute to this beneficial effect, such as drug-induced prostaglandin release potentiating immunosuppressive treatment. Captopril may in fact be the drug of choice for the treatment of SLE patients with severe hypertension.