  We discuss the oscillations effects on neutrinos in the early Universe and
update the cosmological constraints on the oscillation parameters. It is shown
that sterile LOW solution to the solar neutrino problem is almost completely
excluded from cosmological nucleosynthesis considerations. Two possibilities
for the relaxation of this constraint are discussed: high primordial helium-4
yield and a relic lepton asymmetry present at nucleosynthesis epoch. The
numerical analysis proved that Y_p=0.25 only relaxes the constraint on LOW
solution, while L > 10^{-5} is capable to remove it.

High Energy Physics - Phenomenology;Astrophysics