A sizeable difference in the differential production cross section
of top and antitop quarks, respectively, is predicted for
hadronically produced heavy quarks.
It is of order $\alpha_s$ and arises from the
interference between charge odd and even amplitudes respectively.
For the TEVATRON it amounts up to 15\% for the differential
distribution in suitable chosen kinematical regions.
The resulting integrated forward-backward asymmetry of
4–5\% could be measured in the next round of experiments.
At the LHC the asymmetry can be studied by selecting
appropriately chosen kinematical regions.
Furthermore, a slight preference at LHC for centrally
produced antitop is predicted, with top quarks more abundant at
large positive and negative rapidities.