A new kind of calorimeter, commercialized by Setaram SA, appeared two years ago: the differential calorimeter DRC(R). This calorimeter is operated in isoperibolic mode, it was developed by Aventis Pharma in their own laboratories and was based on the work of Baumgartner and Duhaut, Bull. Soc. Chim. France (1960) 1178, and Kussner, Chem. Ing. Techn. 61 (1989). The heat transfer value UA and heat capacities of the reactor contents Cp-MR are determined simultaneously. A description of this new calorimeter and its principles are described in this paper. The simple calibration procedure and the assessment of the reaction heat capacity are presented. (C) 2002 Elsevier Science Ltd. All rights reserved.