  The coupling of space-time torsion to the Dirac equation leads to effects on
the energy levels of atoms which can be tested by Hughes-Drever type
experiments. Reanalysis of these experiments carried out for testing the
anisotropy of mass and anomalous spin couplings can lead to the till now
tightest constraint on the axial torsion by $K \leq 1.5 . 10^{-15} m^{-1}$.
