Based on a new thermopile heat power sensor, which was developed in MEMS technology, a miniaturized flow-through calorimeter was constructed. The heat power sensor consists of a silicon chip with a thin film BiSb/Sb thermopile and a PMMA reaction chamber. To ensure high signal resolution the heat power sensor is mounted inside a high-precision thermostat, which has a temperature stability of less than 100 mu K. The heat power sensitivity of the calorimeter is 4-7 V W-1 depending on the thermal conductivity of the liquid, the height of the chosen reaction chamber and the volume flow rate. A limit of detection of less than 50 nW can be obtained for volume flows lower than 5 mu l min(-1). An important advantage is the low sample consumption of the calorimeter. For special applications the sample need for one measurement pulse does not exceed 20 mu l. (c) 2005 Elsevier B.V. All rights reserved.