  We examine in detail the changes in the production of primordial helium
resulting from nonthermal neutrino momentum distributions produced by resonant
transformation of electron-type neutrinos to steriles. These transformations,
anti-nu_e -> anti-nu_s (nu_e->nu_s), amplify a positive (negative) lepton
number asymmetry. We find that the resulting supression relative to a thermal
distribution of low energy nu_e reduces n -> p conversion to a greater extent
than does the enhancement of n -> p from an identical suppression of anti-nu_e.
Thus, equal lepton-number asymmetries of opposite sign have unequal effects on
the resulting helium yield in primordial nucleosynthesis.
