We performed a series of five baboon experiments to compare cerebral blood flow measured with an improved stable xenon/CT method and the radiolabelled microsphere technique at a PaCO2 of 40 mm Hg. The xenon/CT method was implemented by fitting the arterial xenon uptake with a double exponential function, by measuring the oxygen and carbon dioxide concentrations continuously during each breath and by taking into account the lung-to-brain transit time of xenon. The time of xenon inhalation was extended to 30 minutes to obtain more reliable estimates of CBF in white matter regions. The results indicate an overall correlation coefficient of 0.92 between the two methods and good numeric agreement.