Aims: To design and build a thermoresistometer, named Mastia, which could perform isothermal and nonisothermal experiments. Methods and Results: In order to evaluate the thermoresistometer, the heat resistance of Escherichia coli vegetative cells and Alicyclobacillus acidoterrestris spores was explored. Isothermal heat resistance of E. coli was characterized by D-60 degrees C = 0.38 min and z = 4.7 degrees C in pH 7 buffer. When the vegetative cells were exposed to nonisothermal conditions, their heat resistance was largely increased at slow heating and fast cooling rates. Isothermal heat resistance of A. acidoterrestris was characterized by D-95 degrees C = 7.4 min and z = 9.5 degrees C in orange juice. Under nonisothermal conditions, inactivation was reasonably well predicted from isothermal data. Conclusions: The thermoresistometer Mastia is a very suitable instrument to get heat resistance data of micro-organisms under isothermal and nonisothermal treatments. Significance and Impact of the Study: The thermoresistometer Mastia can be a helpful tool for food processors in order to estimate the level of safety of the treatments they apply.