A thermocell consisting of a rotating disk electrode and another wire electrode in an electrolytic solution is described. The temperature difference is produced by mounting a heater inside the rotating disk electrode while the temperature of the bulk solution is kept constant at a mean temperature of 21°C. The change of the thermoelectric power &egr; for 0.1 and 1.0 N aqueous KCl solution with Ag/AgCl electrodes was independent of the speed of rotation below 375–400 rpm (laminar flow range). At speeds >400 rpm, the &egr; values became dependent on the rotation speed, presumably because of increasing turbulence of the liquid. In the laminar flow range, the mean &egr; values were 185 &mgr;V/deg and 250 &mgr;V/deg for 1.0 N and 0.1 N aqueous KCl solutions, respectively.