  We investigate the Big-Bang Nucleosynthesis constraints on neutrino mixing in
the framework of the two four-neutrino schemes that are favored by the results
of neutrino oscillation experiments. We discuss the implications of these
constraints for terrestrial short and long-baseline neutrino oscillation
experiments and we present some possibilities of testing them in these
experiments. In particular, we show that from the Big-Bang Nucleosynthesis
constraints it follows that the nu(mu)->nu(tau) transition is severely
suppressed in short-baseline experiments, whereas its oscillation amplitude in
long-baseline experiments is of order 1. We also propose a new parameterization
of the four-neutrino mixing matrix U which is appropriate for the schemes under
consideration.
