  The magnetic moment of tau neutrinos in the MeV mass range may be large
enough to modify the cosmological freeze-out calculation and determine the
tau-neutrino relic density. In this paper we revisit such a possibility. We
calculate the evolution and freeze-out of the tau neutrino number density as a
function of its mass and magnetic moment. We then determine its relic density,
then calculate its effect upon primordial nucleosynthesis including previously
neglected effects.
