  The most natural MSW neutrino oscillation interpretation of the GALLEX and
other solar neutrino data, which invokes $m_{\nu_\mu}\sim3\times10^{-3}\eV$,
and a general GUT see-saw hierarchy of neutrino masses,
$m_{\nu_{e,\mu,\tau}}\sim (m_{u,c,t})^2/M_U$, suggest that
$m_{\nu_\tau}\sim10\eV$ in agreement with the preference of COBE and other data
on large-scale structure in the Universe for a hot component in the Dark
Matter. The general see-saw model also suggests that neutrino mixing angles are
related to quark mixing angles, which is also consistent with the oscillation
interpretation of the solar neutrino data, and suggests that the forthcoming
CHORUS and NOMAD experiments at CERN have a good chance of observing $\nu_\mu -
\nu_\tau$ oscillations. We present a minimal realization of the general see-saw
hierarchy in the context of flipped $SU(5)$.

High Energy Physics - Phenomenology