The possible role of intrasolar diffusion is examined for the isotopes of He, Ne, and Xe to see if there is a theoretical basis for an empirical mass fractionation relationship between the isotopic compositions of planetary and solar-wind-implanted elements. It is shown that if diffusion is responsible, even in part, for the observed depletion of 4He in the solar wind, then significant fractionation effects across the isotopes of Ne and Xe as well as He can be predicted. It is also shown that isotopic fractionation need not necessarily infer extreme elemental abundance patterns in the solar interior.