The self-association of the tranquilizer chlorpromazine hydrochloride in aqueous solution was studied.. Using isothermal titration calorimetry, the critical micelle concentration and solvent-micelle interactions were evaluated as a function of temperature, ionic strength, and pH. The enthalpy of demicellization, Delta H-demic, was directly measured from the experimental enthalpy values, which showed that the spontaneous demicellization of chlorpromazine hydrochloride is a highly endothermic process under all experimental conditions studied. The thermodynamic parameters were subsequently calculated from the temperature dependent thermograms. At 25 degrees C, the critical micelle concentration was determined to be 3.2 mM at pH 6.5 with a Delta H-demic of 12.5 kJ/mol, a Delta G(demic) of 24.3 kJ/mol, and a T Delta S-demic of -10.1 kJ/mol. Our results suggest that the enthalpy-entropy compensation theory may be applied to these micelles. In addition, using differential scanning calorimetry, a broad endothermic demicellization peak was observed in postmicelle solutions during heating scans at approximately 45 degrees C. Cooling scans revealed a very broad peak centered around 40 degrees C that corresponds to the heat of micellization.