  Cosmology provides interesting information on neutrino mixing models with
sterile neutrinos. In this case non standard BBN effects can be relevant. We
show how the recent measurement of the baryon content from the observations of
CMB anisotropies together with the primordial nuclear abundances measurements
can be used to constrain them. In particular four neutrino mixing models are
potentially at variance with the cosmological observations. We also discuss the
possible scenarios from future experiments.
