The diffusion of radioargon, A37, and of radioxenon, Xe131m, through inert xenon was measured at —78, 0, 57, and 105°C. The apparatus, a Loschmidt cell in which saturation ionization currents were used as a measure of tracer concentrations, yielded diffusion coefficients which are estimated to have an accuracy of about one percent. The intermolecular potentials of Xe–Xe, derived from the present results, agree with those obtained from thermal conductivity data in the same temperature range, but do not agree with potentials derived from second virial coefficients and crystal data. Nor do they agree with potentials derived from viscosity and thermal conductivity data at higher temperatures. It is shown that this lack of agreement is due to the inadequacy of the potential form. The potential well for the rare gases should be narrower than that given by the Lennard-Jones 12–6 potential.