Renal tissue hypoxia may play a major role in the progression of chronic renal disease. Michaely et al. used blood oxygen level-dependent magnetic resonance imaging to test this hypothesis. They found no relationship between renal oxygenation and stage of chronic kidney disease (CKD). However, renal tissue oxygenation may be related not only to the severity of renal disease but also to its underlying etiology. This added complexity confounds interpretation of data obtained from subjects with CKD due to multiple etiologies.