  Thermodynamics of a heavy quark-antiquark pair in SU(3)-QCD is studied both
below and above the deconfinement critical temperature $T_c$. In the quenched
case, a model of the string passing through heavy valence gluons yields a
correct estimate of $T_c$ and the critical behavior of the string tension below
$T_c$. For two light flavors, entropy and internal energy below $T_c$ can be
obtained from the partition function of heavy-light mesons and baryons. To
calculate the free energy of the system above $T_c$, we apply second-order
perturbation theory in the interaction of the quark-gluon plasma constituents
with the static quark-antiquark pair. The results for the entropy and internal
energy, obtained both below and above $T_c$, are compared with recent lattice
data.
