Acridine has been studied by sublimation calorimetry, differential thermal analysis and heat capacity measurements. Using values of the enthalpy of combustion of this compound obtained from the literature, we have been able to determine the experimental value of its resonance energy which is in accord with the theoretical value. Using the enthalpy contributions previously determined, it was possible to calculate the atomization enthalpy of acridine; comparison with the experimental value is very satisfactory.