Male Sprague-Dawley rats were used to investigate renal vascular abnormalities in the maintenance phase of norepinephrine-induced ischemic acute renal failure. In this model uremia peaks in the first 5 days with progressive recovery of renal function which approaches control at 25 days. Renal blood flow returns to normal in the first week. Micropuncture experiments revealed that there was a dual nephron population during the first 3 days of acute renal failure. The majority of proximal tubules had elevated pressures from tubular obstruction. The nephron filtration rate responses in these nephrons were similar to normal if tubular obstruction was relieved, indicating that glomerular filtration dynamics were not impaired. In other nephrons tubular pressures were low, and venting the tubules did not increase nephron filtration. In these nephrons glomerular blood flowed and capillary pressures were reduced. There was no evidence of tubular fluid backleak from 14C-inulin microperfusion. A second vascular abnormality was an absence of renal blood flow autoregulation at 1 week in acute renal failure. The autoregulatory defect could be corrected by renal denervation.