  The value of $\alpha_s (M_Z)$ emerging from the so called global fits based
mainly on the data at the $Z$ peak (and assuming the standard model) is three
standard deviations higher than the one stemming from the low-energy
phenomenology. The corresponding value of $\Lambda_{\rm QCD}$ is very large,
$\sim$ 500 MeV, and is incompatible with crucial features of QCD. If persists,
the discrepancy should be interpreted as due to contributions to the
$Z$-quark-antiquark vertices which go beyond the standard model.
