Renal involvement is uncommon in the hydralazine induced systemic lupus erythematosus syndrome. Six women with hypertension are described who developed an immune complex glomerulonephritis after taking 50-300 mg hydralazine daily for 6 months to 7 years. Associated features were anemia (100%), hypocomplementemia (50%), a positive antinuclear antibody test (100%) and antibodies to double-stranded DNA (66%). All patients were slow acetylators and four had HLA-DR 4 genotype. Renal function deteriorated in all cases. Cessation of hydralazine combined with immunosuppressive therapy resulted in amelioration of the disease. It is likely that the patients had a hydralazine induced lupus glomerulonephritis, or alternatively had an unmasking of an inherent tendency to idiopathic lupus nephritis by hydralazine.