Measurements of oxygen pressure at the renal cortex above superficial glomeruli led to the concept of a highly effective shunt diffusion of blood gases between interlobular arteries and veins. A mathematical model of gas exchange between these vessels fits well for the exchange of CO2, but not as well for O2. A discrepancy of factor 3-4 was dependent upon the assumptions made for the calculation for O2 (diffusion coefficient for water). Borons hypothesis that aquaporins are used as gas channels through cell membranes was established for CO2, not for O2. Up to now anatomical studies did not show aquaporins within the membranes of interlobular vessels. In our mathematical model, extra gas channels are not necessary for CO2 (diffusion coefficient 20 times that of O2), but for O2 it would explain the experimentally obtained data using different methods. Another aspect is: the barrier between interlobular arteries and veins are thin cell membranes of bilipid layers the diffusion coeff. of which is manyfold higher for O2 than in aqueous solutions, this would overcome the discrepancy mentioned and would explain the facilitated oxygen shunt diffusion in the renal cortex, which is a prerequisite to select the kidney for the effective regulation of the renal erythropoietin production. The support of G.Gros and C. Geers-Knörr is acknowledged as well as the valuable discussion with R.Baumann.