  The next-to-leading order analysis for the cross section for hadroproduction
of top quark pairs close to threshold is presented. Within the framework of
non-relativistic QCD a significant enhancement compared to fixed order
perturbation theory is observed which originates from the characteristic
remnant of the 1S peak below production threshold of top quark pairs. The
analysis includes all color singlet and color octet configurations of top quark
pairs in S-wave states and, for the dominant configurations, it employs
all-order soft gluon resummation for the hard parton cross section. Numerical
results for the Large Hadron Collider at $\sqrt{s} = 14 $TeV and $\sqrt{s} = 10
$TeV and also for the Tevatron are presented. The possibility of a top quark
mass measurement from the invariant mass distribution of top quark pairs is
discussed.
