Endothelin 1 (ET-1) production was examined in the rabbit nephron in acute renal failure (ARF) induced by uranyl acetate administration or by clamping the renal artery. Uranyl acetate dissolved in saline was injected intravenously at a dose of 0.8 mg/kg (n = 12). In the ischemic kidney experiment, 60 min of left renal artery clamping was carried out 1 week after removing the right kidney (n = 8). Plasma and urine concentrations of ET-1 were measured 0, 24, and 48 h after treatment, and immunohistochemical studies of renal tissues obtained 48 h after the experiments were carried out using ET-1 monoclonal antibody. The fractional excretion of ET-1 increased from 10 to 89% at 48 h in the uranyl acetate treated group and from 6 to 15% at 24 h in the renal artery clamping group, suggesting the existence of ET-1 secretion from the nephron in both types of ARF. By immunohistochemical examination, strong ET-1 expression was noted only in the collecting ducts. No staining was observed in other parts of the nephron in both types of ARF. The present study indicates that the increased expression of ET-1 probably reflects production by the collecting ducts in both rabbit ARF models.