The aim of this study was to gage the magnitude of changes of the apparent renal medullary transverse relaxation time (ΔT2*) induced by inhalation of pure oxygen (O2) or carbogen (95% O2, 5% CO2) versus baseline breathing of room air. Eight healthy volunteers underwent 2D multi-gradient echo MR imaging at 1.5 T and 3.0 T. Parametrical T2* relaxation time maps were computed and average T2* was measured in regions of interest placed in the renal medulla and cortex. The largest T2* changes were measured in the renal medulla, with a relative ∆T2* of 33.8 ± 22.0% (right medulla) and 34.7 ± 17.6% (left medulla) as compared to room air for oxygen breathing (p > 0.01), and 53.8 ± 23.9% and 53.5 ± 33.9% (p < 0.01) for carbogen breathing, respectively at 3 T. At 1.5 T, the corresponding values were 13.7 ± 18.5% and 24.1 ± 17.1% (p < 0.01) for oxygen breathing and 23.9 ± 17.2% and 38.9 ± 37.6% (p < 0.01) for carbogen breathing. As a result, we showed that renal medullary T2* times responded strongly to inhalation of hyperoxic gases, which may be attributed to the hypoxic condition of the medulla and subsequent reduction in deoxyhemoglobin. Copyright © 2012 John Wiley & Sons, Ltd.