Titration calorimetry was employed to measure the critical micelle concentration (cmc) and the heat of demicellization Delta H-demic of the four surfactants octyl glucoside, sodium dodecyl sulfate (SDS), sodium cholate, and sodium deoxycholate at temperatures between 10 and 70-80 degrees C. From these data, the thermodynamic parameters Delta G(demic), Delta S-demic, and Delta C-p,C-demic associated with the demicellization process were calculated. Titration calorimetry has the advantage that the cmc and the thermodynamic parameter Delta H-demic can be directly measured, whereas with other methods Delta H-demic has to be calculated from the temperature dependence of the cmc, which requires high precision for the cme data. Changes in temperature caused large variations of Delta H-demic and Delta S-demic, whereas Delta G(demic) remained virtually constant. Therefore, the changes in enthalpy and entropy almost completely compensate each other. At room temperature, the entropy was found to be the dominant factor responsible for micellization, whereas at elevated temperatures contributions from enthalpy dominate. These observations are in agreement with data of other processes where hydrophobic effects play a major role and were used to discuss the nature of the driving forces that rule micelle formation at various temperatures. Furthermore, predictions regarding the degree of hydration of the micelle interior were made. It is shown that titration calorimetry is an easy and fast method to determine the cmc and the demicellization enthalpy from a single experiment. For surfactants with low aggregation numbers the titration curves could be simulated using a mass action model.