  We study bound-state effects on the t\bar{t} production cross section in the
threshold region at hadron colliders. The bound-state effects are important
particularly at the LHC where the gluon fusion is the dominant subprocess. Due
to the formation of t\bar{t} resonances in the J=0 color-singlet channel of gg
\to t\bar{t} and the large width of the top quark, the t\bar{t} invariant-mass
distribution peaks at a few GeV below the t\bar{t} threshold, and it is
significantly enhanced over the naive NLO prediction until several GeV above
the threshold. We present predictions of the t\bar{t} invariant-mass
distribution which incorporate both the bound-state effects and initial-state
radiations up to NLO. The bound-state effects would lead to a substantial
deformation of top-quark kinematical distributions in the threshold region.
