A thermistor electrode to perform in situ calorimetric studies in the range of mK (muW) is developed. Two transient thermal models are used to describe its thermal response. The evaluation of the molar electrochemical Peltier heat is possible by calibrating the amount of the heat supplied by a fine Cr-Ni coiled wire to the thermistor electrode. The thermistor electrode is suitable to measure thermal effects on electrochemical reactions taking place on rather small immobilized metal hexacyanoferrate microparticles (5 x 10(-9)-5 x 10(-8) mol).