A reaction calorimeter has been used to determine at three different temperatures the enthalpy values for the polymerization of pyrrole dissolved in acetonitrile, by using FeCl3 as the oxidative agent. From the calorimetric data it has been found that the reaction is first-order with respect to the pyrrole. The rate constants at the same temperatures have also been determined. By using the Arrhenius equation we have obtained the activation energy for the formation of this electroconducting polymer.