  We report on the determination of $|V_{cb}|$ from the comparison of the
semileptonic inclusive decay rates of B-- and D--mesons using the heavy quark
symmetry of QCD. While the renormalization scale ambiguity does not allow for a
reliable estimate of the quark masses, it almost cancels in the prediction for
$|V_{cb}|$, which reads $|V_{cb}|(\tau_B/1.49\,{\rm ps})^{1/2} = 0.036\pm
0.005$, where the error stems from the uncertainty in the kinetic energy of the
heavy quark inside the meson, in the experimental branching ratios, in QCD
input parameters, and from scale uncertainties. This talk is based on research
work done in collaboration with Patricia Ball.
