An experimental method is described for observing the energy phenomena accompanying elastoplastic deformation, in order to take them into account when identifying a behaviour law. After the energy balance has been considered, the relationships between the dissipation, the stored energy of cold work and the hardening state variables are reviewed. The dissipation is measured continuously during monotonic tensile tests, using microcalorimetry techniques. We describe the experimental arrangement using physical hypothesis and mathematical modelling which allow us to relate the dissipated energy to the signal given by the microcalorimeter. The calibration protocol and some results on two materials are presented. In spite of the spread in experimental results, criteria can be stated for controlling the energy consistency of models. Finally the large discrepancy between energy predictions of certain classical behaviour laws and the stored energy measurements is indicated.