New relative measurements of the viscosity of xenon at a pressure P=1 atm and in the temperature range T=25-700°C are reported. The viscosity of argon has also been remeasured. A careful analysis of the long-term reproducibility of the oscillating-disk viscometer employed in the work is presented together with best estimates of the viscosity of all the noble gases. Standard reference values of the viscosity of the gases at atmospheric pressure and at zero density at 25°C are given. The data for all the monatomic gases are represented by means of a single empirical correlation.