We experienced three cases of malignant hypertension. Plasma endothelin-1 (ET-1) was extremely high in all patients on admission (12.1 +/- 1.0 pg/ml, normal 1.5 +/- 0.5 pg/ml), and changed in parallel with the serum creatinine level. In one patient, during the recovery period, serum creatinine increased 1 mg/dl over a one-week period just after the increase of plasma ET-1 (14.2 pg/ml), while plasma renin activity (PRA) and plasma aldosterone concentration (PAC) were stable. In contrast, the decline of renal dysfunction was larger in patients with high PRA and PAC. These data suggest that increased plasma ET-1 and an enhanced renin-aldosterone-angiotensin system act together in a vicious cycle to deteriorate renal function in patients with malignant hypertension.