Refractive index measurements have been carried out on fluid xenon isochores from 299K to the coexistence temperatures. The mean value of the Lorentz-Lorenz function in the range 5-15 k mol m^-3 is 10.524 mu m³ mol^-1 ( lambda =589.3 nm). The results indicate that (a), the Lorentz-Lorenz function for xenon does not vary by more than +or-0.5% throughout the fluid range, (b) there is no evidence for a large anomaly near T_c, and (c) the temperature dependence of the Lorentz-Lorenz function is small.