  Combining the experimental data on the inclusive decays $D\to X\,e\,\nu$,
$B\to X\,e\,\nu$ and $B\to X\,\tau\,\nu$, we find severe constraints on the
$\bar\Lambda$ and $\lambda_1$ parameters of the Heavy Quark Effective Theory.
In particular, we get $\bar\Lambda<0.7\,$GeV. Our constraints further imply
$m_c\geq1.43\,$GeV and $m_b\geq4.66\,$GeV. We discuss future prospects of
improving these bounds and their phenomenological implications.
