  We analyze the effects of lepton asymmetry on neutrino oscillations and on
cosmological nucleosynthesis with active-sterile oscillating neutrinos. It is
shown that small lepton asymmetries, L < 0.01, whose direct kinetic effect on
nucleosynthesis is negligible, still effect nucleosynthesis considerably
through their influence on oscillating neutrinos. Two different cases of lepton
asymmetry are discussed: an initially present and a dynamically generated in
oscillations. Dynamically generated in resonant oscillations asymmetry at small
mixing angles suppresses oscillations, hence, the nucleosynthesis bounds on
neutrino mass differences at small mixings are relaxed. Initially present
asymmetry may suppress or enhance oscillations. The enhancement is a result of
interchanging resonances between neutrino and antineutrino ensembles due to
resonance waves passing through the neutrino and antineutrino spectrum. Updated
nucleosynthesis bounds on neutrino oscillation parameters accounting for lepton
asymmetry are presented.
