The most striking feature of the oxygen supply to the mamma-lian kidney is its inhomogeneity. The total flow of blood to the kidney per minute is high in relation to its weight. Oxygen extraction across the kidney is so low and mixed renal venous blood so oxygenated that it is often assumed that under normal circumstances kidney cells are plentifully supplied with more than enough oxygen to perform their work. However, the bulk of this supply is directed to the renal cortex, where it maximizes flowdependent clearance of wastes. By contrast, blood flow to the renal medulla is parsimonious. The supply of 02 to the renal medulla barely exceeds its 02 utilization, as illustrated in Table 1 [1]. The striking inhomogeneity of oxygen supply that character-izes the kidney has important implications for renal pathophysi-ology and disease [1—3].