For a sample in an open system (e.g. the vacuum of the electron microscope) the mass flux leaving the sample due to either sample evaporation, sublimation or thermal degradation will be uniquely controlled by the sample temperature. Classical kinetic theory shows that the mass flux rate depends on sample temperature and vapour pressure. By measuring the local rate of mass loss one can thus arrive directly at the local specimen temperature. Moreover, temperature-dependent kinetics of the phase change from the condensed phase to the vapour phase may be used to determine the local sample temperature over a continuous range of temperature due to heat input to the sample from the sample stage environment and the incident electron beam.