An instrument for simultaneous differential scanning calorimetry/synchrotron powder X-ray diffraction was used to detect and quantify the beam-heating effect, i.e. the deposition of measurable energy into a sample by a synchrotron X-ray beam. For beam energy of 17 keV, incident beam flux of 4.27 x 10(11) photon/s, and beam size of 1000 mum x 300 mum, the measured power input into the sample is on the order of 1 mW. The ability to deliver the energy in the form of an almost ideal square-wave made it possible to accurately analyze the response of the differential scanning calorimeter to such an input. The beam-heating effect needs to be considered in performing and evaluating differential scanning calorimetry measurements involving synchrotron X-ray sources.