A patient with a single kidney and oliguric renal failure for 47 days experienced dramatic restoration of glomerular filtration and renal function following graft bypass of an occluded renal artery. There was very little evidence of acute tubular necrosis. The case emphasizes the importance of the renal collateral circulation in the maintenance of tissue viability, even when the hydrostatic pressure of collateral flow is inadequate for glomerular ultrafiltrate formation. The differentiation of oliguric renal failure due to renal arterial occlusion from that due to acute tubular necrosis following arterial injection of radiocontrast material is imperative because of the dramatic response to reconstructive vascular surgery.