We investigate the prospects to observe effects of transverse polarization of top quarks in . QCD absorptive parts generate a polarization of top quarks and antiquarks transverse to the production plane in the partonic processes and , which reaches values of a few percent. These perturbative QCD effects are decreased at the hadronic level. A measurement through momentum correlations among the and decay products will be difficult both at an upgraded Tevatron and at the LHC.