  We discuss a consequence of time reversal symmetry on thermoelectric effect
in nonequilibrium coherent quantum transport. Starting with a quantum version
of the fluctuation theorem, we show that there exist universal relations
between the Peltier coefficient and the Seebeck coefficient of general
mesoscopic systems with Coulomb interaction in a nonlinear regime. This
extended Kelvin-Onsager relation may be used to obtain useful information on
heat current, e.g. the nonlinear Peltier coefficient, which is difficult to be
measured in a usual setup of experiments, only from electric current
measurement.
