  Only small regions in the $m_{t} - \tan\beta$ plane are allowed when
considering simultaneously (assuming the MSSM) coupling constant unification
and (minimal) GUT relations among Yukawa couplings (i.e., $h_{b} = h_{\tau}$ at
the unification point). In particular, if $m_{t} \simle 175$ GeV we find that
only $1 \simle \tan\beta \simle 1.5$ or $\tan\beta \simgr 40 \pm 10$ is
allowed. The former implies that the light Higgs boson is $\simle 110$ GeV and,
in principle, visible to LEPII. The prediction for the Higgs boson mass in the
$\tan\beta \approx 1$ scenario is discussed and uncertainties related to ($i$)
vacuum stability constraints, ($ii$) different methods for calculating the
Higgs boson mass, ($iii$) two-loop calculations and ($iv$) GUT corrections are
briefly reviewed. It is shown that large left-right mixing between the
$t$-scalars can significantly enhance the Higgs boson mass. That and an
ambiguity in the size of the two-loop correction lead to our conservative upper
bound of 110 GeV. Vacuum stability considerations constrain the $t$-scalar
mixing and slightly diminish the upper bound (depending on the value of
$m_{t}$). Improved two-loop calculations are also expected to strengthen the
bound.
